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Hello All - am hoping the knowledge bank here may be able help. I'm resurrecting a John Deere LT166 lawn tractor with 16HP Briggs engine. It has sat for 2-3 years but was running fine, save for a snapped deck belt, previously. I've stripped and cleaned the carb and got it started, driving and mowing, but not very well. It basically won't run properly without choke. I've double checked the jets in the carb. I can just about get it to tick over without choke by adjusting the fuel screw, but it won't rev and it's obviously running far too rich. In any other position it won't even idle, or only for 10-15 secs before stuttering and dying. With choke it will rev, but is maybe at 30% power and clearly not running as it should. Oddly it can manage forwards, but reverse pretty much kills it.

Have I missed something on the Aisan carb? I thought maybe a fuel pump issue but if it runs at full revs, albeit it badly, it can't be? I've checked the tank cap breather as well. It has clean fuel, albeit mixed with whatever small amount of bad might have previously been in the tank, but I think it was bone dry. Is there a hidden jet anywhere on those carbs?

Thanks in advance...!

Wurzel said:

It basically won't run properly without choke.

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Engine wants more fuel.

Wurzel said:

I've double checked the jets in the carb

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Even the sometimes hidden or hard to reach pilot jet?

Have you checked and cleaned the emulsion tube?

Wurzel said:

I can just about get it to tick over without choke by adjusting the fuel screw, but it won't rev and it's obviously running far too rich.

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Is the choke stuck on?

Wurzel said:

Have I missed something on the Aisan carb?

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I would say yes. Sitting for a couple years, the carb needs to be COMPLETELY opened up and probably boiled out. You've missed something inside. Or buy a new carb. Done deal.

Wurzel said:

I thought maybe a fuel pump issue but if it runs at full revs, albeit it badly, it can't be?

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Have you pulled the hose AT the carb fuel bowl inlet? Verified good steady flow from tank? Drain into a glass jar so you can see what is going on.

I would pull and flush the fuel tank. Most likely full of dirt and grass which hinders flow.

Wurzel said:

I've checked the tank cap breather as well.

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Please explain this procedure? Curious......

Wurzel said:

It has clean fuel, albeit mixed with whatever small amount of bad might have previously been in the tank, but I think it was bone dry.

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Dump the tank completely. Get fresh today fuel in there, no E-10 if possible. Fuel stabilizer is your friend. Let's see, when did I get mower gas last??? I personally forgot what I had for dinner last night.

Wurzel said:

Is there a hidden jet anywhere on those carbs?

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I covered this above. Yes there is.

Thanks for your pointers @slomo !

I'll double check fuel supply and also drain and refresh the tank so can be sure there - I've run with the tank cap on and off as well. Choke definitely not stuck on, I'm watching it at the carb. I'll take the carb apart a third time and make a note of each jet, tube and valve cleaned, my slight concern is that emulsion tube. I can't remember if I've done it as looking at the diagram (142), it looks like it's in the tube next to the main jet tube which is under a welch plug? If it is, I definitely haven't.

It is running lean if carburetor needs choke. Clean the carburetor again. Every passage poke with tiny wire, carburetor cleaner and compressed air. Get the emulsion tube out if it is removable. If that doesn’t work, order an aftermarket carburetor by model number.

142 is the emulsion tube. It has super tiny holes so be thorough. Use a magnifying glass and fishing line to verify holes are open. Start saving bread ties. They have small gauge wire under that plastic coating. I found a couple that work great for this. You might have to use a radiator hose angled pic tool to get the emulsion tube out.

Wear safety glasses when spraying carb cleaner. Face shield even better. That stuff burns the eyes let me tell you.

Your carb appears to be maybe a Walbro LMT and Briggs quit using it and went to the Nikki and ruxing carbs.
It's worth your effort to try to stay with the Walbro LMT because it's the most user friendly carb to repair and the smoothest running when all is correct.
I'll post below couple links, one is how to repair a Warlbo LMT link and the other is to view one for sale on flea bay. You have to keep a heads up because some call the Nikki carbs and kits Walbro just to trick you into buying the Nikki stuff.
Their are two type of them Walbro LMT's for attempting to remove the emulsion tube. One has a little main brass jet in the side of the that must be removed first. This type usually have the solenoid on bottom of bowl. The other type does not use this main jet on the side.
It's very important to use a correct fitting Hollow ground screwdriver (gunsmith's type screwdriver) when attempting to remove the emulsion tube and some of them have to be reduced in width on their sides so as to fit down inside the hole by grinding. If too wide the screwdriver will ruin the threads in the hole as it's turned A regular tapered screwdriver will usually ruin the screwdriver slot and the emulsion tube cannot be removed.
If a emulsion tube is stuck and cannot be removed I have as a last attempt effort to get the carb to run is use a Ultrasonic with heater water and white vinegar then high pressure air. The emulsion tube has several tiny holes and if any are clogged the carb no go. when re-installing a emulsion tube just get it snug, then back off and re-snug.
You can get a Nikki China clone as replacement for around $15, but getting one to run correctly is usually a roll the dice. If you have Amazon Prime you can use a free return if it don't run correctly.
Engine model, type, and code will be good for us to reference for more detail.
Carb repair link
https://outdoorpowerinfo.com/repairs/

Walbro LMT on fleece bay

Carburetor for Briggs & Stratton 696179 Original Walbro LMT Replaces Nikki Carb | eBay

Find many great new & used options and get the best deals for Carburetor for Briggs & Stratton 696179 Original Walbro LMT Replaces Nikki Carb at the best online prices at eBay! Free shipping for many products!

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Love the gunsmith screwdriver mention. Make sure the slot fits snug and doesn't hurt the threads.

Take a sanding roll and make your own if you don't have a good fitting flat blade. Use a larger driver than required. Sand away the tip in a parallel fashion. Then grind the sides off to fit the hole.

So have had the carb out again, also emulsion tube out this time as well, but it was already clean. I found three tiny holes just on the air side of the fuel screw hole which I thought might have been blocked, but they're clean as well. All back together and same problem - it will tick over without choke but won't rev at all. I haven't dumped the fuel yet, that's next but it is revving Ok with choke so will see if it has an effect.

@Forest#2 it says it's as Aisan carb, are they rebranded Walbro LMTs? It has the solenoid that also keeps the bowl on, and the little jet on the side perpendicular to the main jet, pics attached (jets removed).

Still no details on the pilot circuit. Even at mid and higher revs, it still pulls fuel combined with the main jet. Does yout carb have a pilot screw of either fuel or air for adjustments?

Your engine wants more fuel. Revs better with the choke on from what you are saying. Find out why you lack fuel delivery.

What does your float height look like? Put the float back in and take some pictures.

Verify you have a good flow of fuel AT the carb inlet pipe.

Lastly IF the carb says Aisan and OEM is a Walbro, something is off there.

There's more to it than a clean main jet and emulsion tube. I would enrichen the pilot circuit.

@slomo thanks and agreed I can find no pilot jet and there's no evidence of one on the diagram above, so I don't know how the pilot circuit works on this carb. It has a fuel mixture screw which I've checked and the tip and seat it sits in are good. It does seem to be ticking over a touch better without choke now than previously, but I can't find a mixture setting that allows it to rev without choke, I've started from half a turn right out to three turns or more.

When I do try to rev without choke the carb chucks fuel forward out of the air side and kills the engine straight away.

Can't take a pic of float height as bowl would be on? Or have I misunderstood? Float is on in the above pic but I can turn it over and support it at closed level if that's what you mean?

Will un-attach fuel inlet with engine running to check the pump is pulling fuel up from the tank, as you mentioned earlier.

I should add this is a UK, not US machine, in case that accounts for the Aisan carb - Googling indicates they were fitted to a few. The engine is model 303777.

Starting to think it might be easier to find an aftermarket carb and hope it works - grass is growing!

I've never seen anything like that carb as being a Walbro.. (in the USA and your engine model number is USA strange. Make sure you do not have a intake manifold air leak. The chole and throttle is slightly different on the USA LMT Walbro's.
Can you post up the complete Model, type and code of your engine?
Dopes it say Briggs on the engine or ????

Am now wondering what it is! It looks like a Vanguard, but is branded John Deere, code plate below and Briggs plate from the other side also pictured.

Will check manifold leak with carb spray but it's pretty snug. I'm struggling with it running flat out on choke, evidently getting enough fuel, then dying when the choke restriction is removed. It actually smells rich the whole time to me but that doesn't make sense.

Video showing choke effect:

Wurzel said:

It has a fuel mixture screw which I've checked

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THAT is the pilot either fuel or air screw. In THAT circuit, sounds as it's clogged. You mentioned half a turn to 3 turns, does nothing. That told me it was not working as it should. REMOVE the pilot screw. Spray carb cleaner in there. Spray compressed air in there. Rod the hole out with fishing line or bread tie. Try to seal the hole with your air nozzle to really force the clog out. Research welch plugs on carbs. You might need to remove one or more to get BEHIND them to get the carb clean.

Wurzel said:

When I do try to rev without choke the carb chucks fuel forward out of the air side and kills the engine straight away.

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What does the flywheel key look like? Are the valves set proper? Remember there are 2 TDC strokes on a 4 cycle engine. Could be set on the wrong stroke. Flywheel key needs to be unmolested and aligned straight up, perfectly. CLEAN the block cooling fins while you are there.

Wurzel said:

Can't take a pic of float height as bowl would be on? Or have I misunderstood? Float is on in the above pic but I can turn it over and support it at closed level if that's what you mean?

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YES, your 3rd picture from the left. Now flip the carb upside down. Look at the float and the mounting surface for the bowl. Float should be parallel to the bowl mounting area. Not hang below nor above.

Wurzel said:

Starting to think it might be easier to find an aftermarket carb and hope it works - grass is growing!

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Easy does it there. Try and get this one going.

That is a Briggs engine.


Carb is no longer available per Jacks Small Engines.

Some of the others here might can find a superseded carb part number??????

Make sure you have full battery voltage AT the carb solenoid wires, key on. That thing "could" be limiting fuel flow into the carb, could be sticking. I always snip those plungers off so as to never have a fuel delivery issue again.

Did you look on the top of BOTH valve covers for complete engine info?

sometimes someone will install a valve cover up side down and the info is not visible.

Also if you decide to remove the welch plugs as a final attempt for good cleaning/rodding of the passages, I've removed welch plugs and re-used the same ones by very carefully drilling a tiny hole in the center, I use a drill stop so as to drill through only the welch plug, then I can carefully pull it out with a o ring pick or a awl then re-form the welch plug on a piece of leather and to seal the hole I have some slow drying two part epoxy that I use AFTER the welch plug is re-installed on the carb. My epoxy is the consistency of majarine or soft butter and will not flow through the hole and I coat the complete welch plug out to it's edges and smooth it out with finger before it completely dries. It's actually Brownells acraglass gel.
Do as slomo says about using high volume compressed air. That is type carb that high pressure air can be used with no concerns about damaging the internals the internals. I sometimes place screen wire cage around a carb before injecting high pressure air so as to catch welch plug if they blow out and become lost.

Here is a link that shows two different carbs and parts list for a 303777 1147-E1
The latter cab 807639 and it's parts kit 807962 is very expensive type.

The earlier 808728 is more reasonable one but they go by engine code numbers for the two different carbs.

https://jackssmallengines.com/jacks...arburetor-fuel-supply-kit-carburetor-overhaul

slomo said:

THAT is the pilot either fuel or air screw. In THAT circuit, sounds as it's clogged. You mentioned half a turn to 3 turns, does nothing. That told me it was not working as it should. REMOVE the pilot screw. Spray carb cleaner in there. Spray compressed air in there. Rod the hole out with fishing line or bread tie. Try to seal the hole with your air nozzle to really force the clog out. Research welch plugs on carbs. You might need to remove one or more to get BEHIND them to get the carb clean.

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I haven't fired compressed air through there yet but it has had a load of carb cleaner through. I'll also try compressed air in case the carb cleaner hasn't moved something, plus a wire guitar string I've found works well. I've pictured the fuel screw port in the venturi below, what do those three just visible (hard to get phone to focus!) behind do? They're connected to 72 in the diagram via a channel (showing in pic 1 top of carb) in the carb body - again all blasted through with carb cleaner and apparently clear.

The fuel screw was doing little previously, but now if I lean it off too much it stalls, so is working at the least in part.

Flywheel - haven't got in that far yet, will check and also do fins if clogged. Valve clearances likewise.

Will also check float level. Disconnecting the solenoid kills the engine, but I'll check the voltage to see if constant. I'm twisting the carb once it's off the engine to unscrew the bowl, as I can't see a way to easily disconnect the solenoid wiring at the solenoid. Twisting the solenoid will have twisted the wire and stressed the connection over time / previous owners I'm sure.

@Forest#2 was there info missing from my last? I will check tomorrow in daylight again. Noted re welch plugs, thanks for the tip!

Appreciate your continued help!

Just to give you a brief idea of their use:
Those ports in the carb throat are called something like transistion ports.
You can re-view such on-line. One is located on the air intake throat above the butterfly of the carb and its the idle port. Air rushing through the throat sucks gas through which ever port the butterfly has opened towards. On the high speed port below the butterfly or engine side when the butterfly is wide open all three will be providing gas by the suction of air rushing past the port/ports.
One of the other two is on the engine side of the butterfly and it's the High speed port that sucks more gas into the engine as the butterfly opens.
The one in the middle might be a trasistion between the high and low butterfly opening.
They all have to be open and yes hard to get to. You have to be careful and not break off a wire in them or you will be SOL. No way of getting the wire/rod back out. One goes to the idle circuit and meets up with others channels under a welch plug. The metering circuits and jets are located inside the carb to regulate the proper amount of gas coming out those posts per the butterfly opening amount and jets sized per HP of the engine, etc. Do not damage those ports.
A hint where this idle welch plug is is it's usually close to the idle jet area if the carb has a adjustable idle jet. I have some long different size needle tips that I can put on my air nozzle gun so as to blow high pressure air back through those ports. The air nozzle kit I have came with a air nozzle and about 6 different screw on tips. It looks similar to this one.

Make sure you have full battery voltage AT the carb solenoid wires, key on. That thing "could" be limiting fuel flow into the carb, could be sticking. I always snip those plungers off so as to never have a fuel delivery issue again.

Right about the ABF (anti back fire) solenoid plunger.

I've heard rumors that they can be tested on the work bench with a good 9v xistor radio battery but I always just use 12v. Make sure the plunger is fully retracting. I have cleaned up sticking plungers by using a oil and just keep on operating the plunger by hand, but if it's sticking just give her the clip/snip.

With workshop facilities still under construction for a couple of weeks I'm a little limited, but nonetheless I did get a bit more done this evening.

Carb: Had the carb off again and got into the transition ports and idle port with fine wire, plus compressed air. I can see clearly through the idle port, but it's impossible to say if one or another of the transition ports may remain partially blocked. I was however able to get plenty of air from the top of 72 (with screw 955 removed), in the diagram below through to the idle port and also out an air side port.

Carb back on and problem remains, however while blowing compressed air, I did see the welch plug above the transition jets (which looks to have been got at before), has a small air leak - which won't be helping. Rudimentarily I've put my finger over it while the engine is running and there's no difference, but even so it will need replacing. Also still need to properly check for any more substantial vaccuum leaks at the manifold.

Fuel: I'm getting a steady 12v at the fuel solenoid and good flow at the carb inlet. I haven't been able to bench test the solenoid yet. Float level checked and good. However having had a better look at the tank there's quite a lot of fuel in it, which means more of it will be old. Once I've found the drain plug, I will drain and refresh - so definitely some hope there.

Mechanical: I haven't seen the fly wheel yet or checked valve clearances, I'll get to those once I've changed the fuel / am not working off a concrete floor!

Typically the pilot circuit works at idle and off idle. Not mid and full throttle. It still draws fuel and air through that circuit when at full revs. Adjusting the pilot screw should either stumble the engine or smooth it out. That is if it's working as it should at low revs.

Old fuel and possible water contamination are definitely something to address first. Stop all testing until you have fresh (non E-10 if possible) gas. Get some Stabil fuel stabilizer and add it to your fuel can. Shake it well. Never worry about bad fuel again.

I would snip the anti-backfire solenoid plunger off. Just idle down the revs and turn the key off. You still might get a pop but it doesn't harm anything. Never worry about starting issues again.

So carb upside down, the float was hanging level with the bowl mating surface? If so that is good.

You might have to strip the carb down and boil it. Is that the OEM original carb, to that engine, you are working with?

Having that much old fuel in the tank (turned out to be about 4l) was a massive oversight given I only put a little fresh in - so I was convinced that would be the issue. But alas after dropping the tank, draining the fuel line and hooking it up to a fresh fuel source, it's made no difference. I do recall at least smelling the tank before I started and it was fine, plus the old fuel had a very red (not brown), tinge - so I think it must have had stabiliser in it.

So I'm back where I started, full revs with choke is no issue, but I can't past a quarter without. It feels like it's getting plenty of fuel without choke though, as it sprays unburnt fuel forward back out the carb as it starts to splutter and die? Fuel screw works at idle, too lean and it stumbles, then it stops having an effect too far the other way, but won't rev at all if too rich. It still doesn't start too well without choke though.

The float valve closes about parallel with the mating service, but upside down IIRC it rests beyond parallel, there's a little slack in float hinge. I will snip the plunger, but that would likely be affecting it with choke as well.

I don't have an ultrasonic cleaner but I think my last option is too boil the carb, maybe it will move something if that's the issue. As far as I can ascertain, it is the OEM carb for that engine, it's exactly as @Forest#2 's diagram on the link above.

I did accidentally leave screw and washer 955 off the carb a couple days ago and started it up. Needless to say there was a massive vaccuum leak and it ran very badly - but it seemed like the same problem but worse. So am wondering if there somehow could be a vaccuum leak somewhere - more testing there. I should add, I'm doing this without the air filter fitted, but it would be a long shot to say that's leaning it out too much?

You say:
It feels like it's getting plenty of fuel without choke though, as it sprays unburnt fuel forward back out the carb as it starts to splutter and die?

Tell us more about what you are saying here??????????
Is this as it's running fast with choke or what are you trying to indicate????

Reason I ask is I'm suspicious of something else as a issue, like maybe you have more than one problem with that engine???????????????

No that's only if it's running fast with choke and i take the choke off, or when I try to rev it more than it wants to go, without choke. It's like a carb backfire. I'll get a video tomorrow to demonstrate!

your Briggs twin Intek engine parts list.
You can also get a service manual for that engine if desired for around $25 TO30. (you might find a freebie download somewhere)
Look for a Briggs Twin OHV, part number might be 273521.

You have a problem with that engine that is not JUST the carb.
I've seen other things very similar to yours make me think it was the carb when it was ignition, timing, bad valves, etc.
You need to check elsewhere.

What I would start checking.
I would install new spark plugs NGK 6130 or champion RC12YC gapped properly.
First I would make sure that the valves on both heads are adjusted properly per specs and I would also look at the valve lift (compare the valve lift to each other) to make sure you do not have a flat or worn cam lobe.
I would make sure the flywheel key is good.

I've seen the single cylinder Briggs engines act like that due to the intake valve lobe worn down and the valve lash even though adjusted properly would not allow the engine to take gas properly. The valve lift should be same on both the exhaust and the intake valves.
Also I would confirm by using a Ohmmeter that both of the diodes in the kill wire harness going to the magnetos are Ok. (one not shorted) You can check on line how to ohm the diodes.
Those are isolation diodes and if one is shorted the ignition will be erratic at different rpms. While checking the diodes check the air gap on both magnetos as at .010-.012.
also make sure the engine is not running on just one cylinder. You can do this by grounding one spark plug wire at a time on each cylinder.
after doing the valve lash I would compare the compression on cylinder 1 to cylinder 2 and see if they are balanced.

Wurzel said:

The float valve closes about parallel with the mating service, but upside down IIRC it rests beyond parallel

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Nope. Needs to be exactly parallel, to the bowl mating flange. Not about parallel nor close to parallel. These little tricks can cause grief. Too low a fuel level will starve the engine. Too high, well you get the email.

Wurzel said:

I will snip the plunger, but that would likely be affecting it with choke as well.

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Go to the hardware store. Get a small bolt, SAME threads as the carb solenoid. Just something to attach the carb bowl on for testing. We are temporarily eliminating the carb solenoid. See if this changes anything. If not, reinstall the solenoid if you want to.

Wurzel said:

I don't have an ultrasonic cleaner but I think my last option is too boil the carb,

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I myself, am not impressed with ultra sonic cleaners for carbs. Maybe some guys have better luck. Now the wife's dishwasher, greatest parts washer on the planet, yes. Good ol' pot scrubber cycle works great. Boiling carbs I feel is the best way to really get inside and do some good. As you can see, the carb is dunked in cleaning solution and the heat loosens gunk up. Strip all plastic parts out first. Lay the jets and emulsion tube in the pan. Bertsmobile1 has shared this tip with us. Summation don't sweat not having an ultra sonic cleaner for this.

If the engine is puking gas out of the carb, we are talking cam timing issues right? Been a while on that trick for my memory. Like a 2 stroke? Or it is a valve adjustment needed? Having a senior moment here...... LOL Flat cam lobe?? Going with a bad cam lobe for 20 bucks Alex.

Pull the valve cover/s and sparky plug/s. Rotate the engine by hand. Watch the rocker arms. Rockers should move roughly the same depth INTO the block. Might have a second small bump on the EX valve for compression release.

So a couple of videos, the first showing it running flat out with about 80% choke, then the effect of removing choke, shown at the carb, where it starts stumbling and dies. The second is it starting at idle with no choke, then trying to gradually introduce revs.

Full revs to no choke: https://youtube.com/shorts/qQAejaOIz8E?feature=share

No choke idle to revs: https://youtube.com/shorts/mOj3QcGQN7k?feature=share

Poorly video'd on my phone so apologies for sound...

Had ocnfirmed by another this evening that it was running OK only a year ago, so I'm struggling to make the jump to a mechanical issue. I'm just bolting and unbolting the carb, will take the shroud off tomorrow and have a clean, is there potential for a vaccuum leak further in than the manifold / carb mating surface?

Hard to tell for sure but I seem to detect that it's only running on one cylinder sometimes maybe. (or one cylinder is weaker) You can judge such by rpm drop as each cylinder is disabled, comparing one to the other.

You can easily confirm such by sliding back the rubber boots on both spark plugs so as to see the metal ends while on the spark plug and while the engine is running at idle ground each spark plug wire one at a time using a long blade screwdriver. If grounding one spark plug wire immediately starts killing the engine that is the ONE CYLINDER that it's using to run.
The cylinder that makes no difference when it's spark plug wire is grounded is the dead or weak cylinder.

Lightly lubing the spark plug wire itself just above the boot helps when sliding the boot back. (another way is to allow a small solid wire to stick out of the boot and ground the wire while it's running.
Just because you see a spark at both plugs IS NOT sure indicator that both cylinders are actually producing power. The other way is to use a fuse puller and momentarily pull the spark plug wire off the plug. I do not like to pull a plug wire for testing while running, I prefer grounding but sometimes I have no other choice.

Wurzel said:

Hello All - am hoping the knowledge bank here may be able help. I'm resurrecting a John Deere LT166 lawn tractor with 16HP Briggs engine. It has sat for 2-3 years but was running fine, save for a snapped deck belt, previously. I've stripped and cleaned the carb and got it started, driving and mowing, but not very well. It basically won't run properly without choke. I've double checked the jets in the carb. I can just about get it to tick over without choke by adjusting the fuel screw, but it won't rev and it's obviously running far too rich. In any other position it won't even idle, or only for 10-15 secs before stuttering and dying. With choke it will rev, but is maybe at 30% power and clearly not running as it should. Oddly it can manage forwards, but reverse pretty much kills it.

Have I missed something on the Aisan carb? I thought maybe a fuel pump issue but if it runs at full revs, albeit it badly, it can't be? I've checked the tank cap breather as well. It has clean fuel, albeit mixed with whatever small amount of bad might have previously been in the tank, but I think it was bone dry. Is there a hidden jet anywhere on those carbs?

Thanks in advance...!

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Are those composite floats or just really crusty brass floats? The composite floats are sometimes like the Bing composite floats and they absorb gas after the surface sealing fails making the float too heavy and the needle never closes. Thus, too rich as you say it appears to be.

slomo said:

142 is the emulsion tube. It has super tiny holes so be thorough. Use a magnifying glass and fishing line to verify holes are open. Start saving bread ties. They have small gauge wire under that plastic coating. I found a couple that work great for this. You might have to use a radiator hose angled pic tool to get the emulsion tube out.

Wear safety glasses when spraying carb cleaner. Face shield even better. That stuff burns the eyes let me tell you.

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The wires on a Wire Brush work well for poking through these holes. Some jets on the bottom of the float bowl have a very tiny hold on an angle in the threads.

I hope you changed out the Fuel Filter.

Wurzel said:

I haven't fired compressed air through there yet but it has had a load of carb cleaner through. I'll also try compressed air in case the carb cleaner hasn't moved something, plus a wire guitar string I've found works well. I've pictured the fuel screw port in the venturi below, what do those three just visible (hard to get phone to focus!) behind do? They're connected to 72 in the diagram via a channel (showing in pic 1 top of carb) in the carb body - again all blasted through with carb cleaner and apparently clear.

The fuel screw was doing little previously, but now if I lean it off too much it stalls, so is working at the least in part.

Flywheel - haven't got in that far yet, will check and also do fins if clogged. Valve clearances likewise.

Will also check float level. Disconnecting the solenoid kills the engine, but I'll check the voltage to see if constant. I'm twisting the carb once it's off the engine to unscrew the bowl, as I can't see a way to easily disconnect the solenoid wiring at the solenoid. Twisting the solenoid will have twisted the wire and stressed the connection over time / previous owners I'm sure.

@Forest#2 was there info missing from my last? I will check tomorrow in daylight again. Noted re welch plugs, thanks for the tip!

Appreciate your continued help!

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Narrow (thin, flat) 1/2" wrench fits at the top of solenoid at bottom of bowl to remove

Wurzel said:

Hello All - am hoping the knowledge bank here may be able help. I'm resurrecting a John Deere LT166 lawn tractor with 16HP Briggs engine. It has sat for 2-3 years but was running fine, save for a snapped deck belt, previously. I've stripped and cleaned the carb and got it started, driving and mowing, but not very well. It basically won't run properly without choke. I've double checked the jets in the carb. I can just about get it to tick over without choke by adjusting the fuel screw, but it won't rev and it's obviously running far too rich. In any other position it won't even idle, or only for 10-15 secs before stuttering and dying. With choke it will rev, but is maybe at 30% power and clearly not running as it should. Oddly it can manage forwards, but reverse pretty much kills it.

Have I missed something on the Aisan carb? I thought maybe a fuel pump issue but if it runs at full revs, albeit it badly, it can't be? I've checked the tank cap breather as well. It has clean fuel, albeit mixed with whatever small amount of bad might have previously been in the tank, but I think it was bone dry. Is there a hidden jet anywhere on those carbs?

Thanks in advance...!

Click to expand...

If it's running rich, most likely the air jets are plugged.

Wurzel said:

Hello All - am hoping the knowledge bank here may be able help. I'm resurrecting a John Deere LT166 lawn tractor with 16HP Briggs engine. It has sat for 2-3 years but was running fine, save for a snapped deck belt, previously. I've stripped and cleaned the carb and got it started, driving and mowing, but not very well. It basically won't run properly without choke. I've double checked the jets in the carb. I can just about get it to tick over without choke by adjusting the fuel screw, but it won't rev and it's obviously running far too rich. In any other position it won't even idle, or only for 10-15 secs before stuttering and dying. With choke it will rev, but is maybe at 30% power and clearly not running as it should. Oddly it can manage forwards, but reverse pretty much kills it.

Have I missed something on the Aisan carb? I thought maybe a fuel pump issue but if it runs at full revs, albeit it badly, it can't be? I've checked the tank cap breather as well. It has clean fuel, albeit mixed with whatever small amount of bad might have previously been in the tank, but I think it was bone dry. Is there a hidden jet anywhere on those carbs?

Thanks in advance...!

Click to expand...

Sounds like a head gasket issue.
Probably got full of thum grass clippings and oil, and ran too hot.
Once the covers been removed of course, things can be observed, flywheel magnet, coil, and any foreign matter trapped in the cooling fins. Some compressed air, or (pressure washing) works, (remove the coil first) to get the gunk off.

Wurzel said:

Hello All - am hoping the knowledge bank here may be able help. I'm resurrecting a John Deere LT166 lawn tractor with 16HP Briggs engine. It has sat for 2-3 years but was running fine, save for a snapped deck belt, previously. I've stripped and cleaned the carb and got it started, driving and mowing, but not very well. It basically won't run properly without choke. I've double checked the jets in the carb. I can just about get it to tick over without choke by adjusting the fuel screw, but it won't rev and it's obviously running far too rich. In any other position it won't even idle, or only for 10-15 secs before stuttering and dying. With choke it will rev, but is maybe at 30% power and clearly not running as it should. Oddly it can manage forwards, but reverse pretty much kills it.

Have I missed something on the Aisan carb? I thought maybe a fuel pump issue but if it runs at full revs, albeit it badly, it can't be? I've checked the tank cap breather as well. It has clean fuel, albeit mixed with whatever small amount of bad might have previously been in the tank, but I think it was bone dry. Is there a hidden jet anywhere on those carbs?

Thanks in advance...!

Click to expand...

Wurzel said:

Hello All - am hoping the knowledge bank here may be able help. I'm resurrecting a John Deere LT166 lawn tractor with 16HP Briggs engine. It has sat for 2-3 years but was running fine, save for a snapped deck belt, previously. I've stripped and cleaned the carb and got it started, driving and mowing, but not very well. It basically won't run properly without choke. I've double checked the jets in the carb. I can just about get it to tick over without choke by adjusting the fuel screw, but it won't rev and it's obviously running far too rich. In any other position it won't even idle, or only for 10-15 secs before stuttering and dying. With choke it will rev, but is maybe at 30% power and clearly not running as it should. Oddly it can manage forwards, but reverse pretty much kills it.

Have I missed something on the Aisan carb? I thought maybe a fuel pump issue but if it runs at full revs, albeit it badly, it can't be? I've checked the tank cap breather as well. It has clean fuel, albeit mixed with whatever small amount of bad might have previously been in the tank, but I think it was bone dry. Is there a hidden jet anywhere on those carbs?

Thanks in advance...!

Click to expand...

A new carb kids only from 10 to 15 bucks I just replace the parts

I have the exact problem with a Kohler SV590 19hp. The governor brackets were previously adjusted and I think I got them close. Almost idles with choke partically on, spits fuel out when throttle increased. More than one OEM carb and one China carb. Mine does have a mixture screw, but little affect. For the cheap price, try another carb and see if problem changes. Like mentioned, Amazon will take the return.

barny57 said:

A new carb kids only from 10 to 15 bucks I just replace the parts

Click to expand...

Having some trouble finding a compatible one, the linkages are top mounted on most of the ones that claim to be replacements...

S.A.P. said:

Sounds like a head gasket issue.
Probably got full of thum grass clippings and oil, and ran too hot.
Once the covers been removed of course, things can be observed, flywheel magnet, coil, and any foreign matter trapped in the cooling fins. Some compressed air, or (pressure washing) works, (remove the coil first) to get the gunk off.

Click to expand...

Yep next job, hopefully not

Gord Baker said:

I hope you changed out the Fuel Filter.

Click to expand...

Not yet, will do but have good flow at carb inlet

RevB said:

Are those composite floats or just really crusty brass floats? The composite floats are sometimes like the Bing composite floats and they absorb gas after the surface sealing fails making the float too heavy and the needle never closes. Thus, too rich as you say it appears to be.

Click to expand...

Could be a thing, they're composite

Whatever happened with this? I'm a little confused if I conflicting statements in the first post. Says they think it's obviously too rich but then when they give it choke it smooths out and runs better but only has 30% power.
Sounds to me like it's actually lean and even with the choke it's not getting enough.
It always irritates me when people , well actually customers, say they cleaned out the carburetor.. blah blah blah, as most people don't really know how to clean out a carburetor properly or don't no what the actual crucial part is to clean.

I got a feeling this carburetor is still gummed up and that's the problem. So where does it stand now?

From your post #24
You say
as it sprays unburnt fuel forward back out the carb as it starts to splutter and die? Fuel screw works at idle, too lean and it stumbles,.

Did you ever check to see if the engine will idle/run using only one cylinder doing the cylinder comparison test suggested previously?
Listening to your video in post #30 you could easily do such with the engine idling.
Also
Did you ever check the valve lash?

If you remove the shroud keep a heads up and do not run the engine long enough to overheat

How many times have we heard the story, it was running good when I parked it, therefore the engine will run great when a battery is installed, trust me.

Wurzel said:

So a couple of videos, the first showing it running flat out with about 80% choke, then the effect of removing choke, shown at the carb, where it starts stumbling and dies. The second is it starting at idle with no choke, then trying to gradually introduce revs.

Full revs to no choke: https://youtube.com/shorts/qQAejaOIz8E?feature=share

No choke idle to revs: https://youtube.com/shorts/mOj3QcGQN7k?feature=share

Poorly video'd on my phone so apologies for sound...

Had ocnfirmed by another this evening that it was running OK only a year ago, so I'm struggling to make the jump to a mechanical issue. I'm just bolting and unbolting the carb, will take the shroud off tomorrow and have a clean, is there potential for a vaccuum leak further in than the manifold / carb mating surface?

Click to expand...

Your videos indicated it ran fine at idle and low revs. Pilot circuit seemed okay there. Just when you increased throttle is ran short on fuel. So the main jet is to be looked at. You need choke for higher revs. That also confirms you are shy on fuel from the main jet.

Remove the main jet. Look for a jet number on it and see if your parts schematic lists any jet sizes. You might have to SLIGHTLY open up that main jet. Just a little bit at a time.

I would verify no vacuum leaks prior to enlarging the main jet size.

RevB said:

Are those composite floats or just really crusty brass floats? The composite floats are sometimes like the Bing composite floats and they absorb gas after the surface sealing fails making the float too heavy and the needle never closes. Thus, too rich as you say it appears to be.

Click to expand...

His engine is starving for fuel. He has to choke it to smooth it out in high revs.

Forest#2 said:

Hard to tell for sure but I seem to detect that it's only running on one cylinder sometimes maybe. (or one cylinder is weaker) You can judge such by rpm drop as each cylinder is disabled, comparing one to the other.

You can easily confirm such by sliding back the rubber boots on both spark plugs so as to see the metal ends while on the spark plug and while the engine is running at idle ground each spark plug wire one at a time using a long blade screwdriver. If grounding one spark plug wire immediately starts killing the engine that is the ONE CYLINDER that it's using to run.
The cylinder that makes no difference when it's spark plug wire is grounded is the dead or weak cylinder.

Lightly lubing the spark plug wire itself just above the boot helps when sliding the boot back. (another way is to allow a small solid wire to stick out of the boot and ground the wire while it's running.
Just because you see a spark at both plugs IS NOT sure indicator that both cylinders are actually producing power. The other way is to use a fuse puller and momentarily pull the spark plug wire off the plug. I do not like to pull a plug wire for testing while running, I prefer grounding but sometimes I have no other choice.

Click to expand...

Feel or measure the temps from both exhaust pipes directly off the heads. Both should be hot.

From your post #24
You say
as it sprays unburnt fuel forward back out the carb as it starts to splutter and die? Fuel screw works at idle, too lean and it stumbles,.

Did you ever check to see if the engine will still idle using only one cylinder doing the cylinder comparison test suggested.
Listening to your video in post #30 you could easily do such with the engine idling.
Did you ever check the valve lash?

Feel or measure the temps from both exhaust pipes directly off the heads. Both should be hot.

I've got a IR thermometer that is really good for fast checking for a cold dead cylinde or comparing cylinder temps..

Progress at last thanks to your pointers, it's only running on one cylinder, #1 is down.

The plugs are in a very different condition, the one on #1 cylinder having done little to no work. Swapped the plugs with each other and #1 still not firing, tested and confirmed no spark on #1.

Forest#2 said:

Also I would confirm by using a Ohmmeter that both of the diodes in the kill wire harness going to the magnetos are Ok. (one not shorted) You can check on line how to ohm the diodes.
Those are isolation diodes and if one is shorted the ignition will be erratic at different rpms. While checking the diodes check the air gap on both magnetos as at .010-.012.

Click to expand...

Checked #1 magneto and the gap was too big, set correctly but still no spark. Have now run out of light, but initial tests with multimeter suggest the kill diode on #1 magneto is open. Will test properly tomorrow to confirm - thanks again for all your help!

The coil Gap is pretty forgiving on those. Just use a business card or whatever but most of them will fire just fine even at the widest position and it's more important to make sure it doesn't rub on the flywheel but a few thousands here or there is not going to cause a no spark condition.

If you actually have no spark jumping from The wire to the engine block or on a good known plug where it won't jump the plug gap then you certainly need to figure out the no spark condition for that one.

Just couple tips:

A OPEN diode will not keep the magneto from firing. A shorted or low resistance diode will result in erratic/misfire operation. The diodes purpose is as isolation diodes, isolating one mag from the other when the engine is running. I've replaced those diodes with a 1N4007, 1 amp, 1000PIV (peak inverse voltage) buying them dirt cheap on fleece bay. I just cut the wire leads on the old ones out of the wire loom, solder or crimp in the replacements and use heat shrink tubing over the replacements instead of buying the Briggs diode harness. If that diode is burned open or charred it's due to voltage getting onto the kill wire and on mowers that have been setting long time outside water gets into the ignition switch and rust inside will allow cross tracking of voltage. If you loose the/a magneto again later you will need to replace the ign switch. Be sure you get the polarity correct on the replacement diode when installing (the white line ring or cathode will go towards the magneto)

Those magnetos can be found for less than $20. I've had good luck with the ones from Amazon and fleece bay. I try to keep a spare magneto around. I've have previously bought the $70 Napa mag replacements and have them fail within a years time.
I would at the very least replace both magnetos, set the air gap at .010-.012 (most plastic cards are too thick at .015) Air gap is not real critical just make sure you have clearance to the magnet after setting by turning the flywheel by hand. Save the one that's firing as a spare maybe.
Then replace the one diode or wire harness. Be careful BEFORE trying to turn out the 5/16 machine screws holding the mags. That is steel screws into aluminum and they will twist off easily, FIRST slightly/lightly peck on their head with a small hammer and the vibration will loosen the corrosion. Make sure you get them just good snug when going back. I sometimes use little bit of Anti-seize on their threads.
You cannot make any logical ohmmeter tests on those mags because their is electronic sealed inside. The real test is to use a old spark plug and set the gap at approx .060 and look at the spark in shade or a darkened room.

I would also pull both valve covers and check the valve lash before ordering parts. Might need valve cover gaskets after doing so. You can find specs for such on-line.

BUT before jumping in and buying mag's and diodes even though you do not see spark. I would compare compression on each cylinder. Most likely ok but now is the time to test such. You will be mainly checking to see if valves and valve seats are Ok. The heads on some of those Briggs OHV's will bite the dust in a surprise way and no or weak compression.

It appears you had two issues going in, clogged carb and a weak or dead cylinder, maybe.
But it was running good when stored. (Murphy's law strikes again)

Just to clarify things
The magnetos have a Hall Effect Trigger chip in them which is what makes them work
They have a kill wire attached to stop them working when you shut down .
On twin cylinder engines you get a ripple down the kill wire that can interfear with the other magneto so they put diodes in there to clamp this signal.
On B & S engines the diode is usually in the kill wires and quite obvious.
Thses can be replaced for a few cents or the sub loom can be replaced for a lot of dollars .
The chip inside the magneto coil is neither repairable nor replaceable ( I have pulled a few apart ) .
So you test the coils by removing the kill wire
No spark with the kill wire removed = dead coil that has to be replaced

bertsmobile1 said:

Just to clarify things
The magnetos have a Hall Effect Trigger chip in them which is what makes them work
They have a kill wire attached to stop them working when you shut down .
On twin cylinder engines you get a ripple down the kill wire that can interfear with the other magneto so they put diodes in there to clamp this signal.
On B & S engines the diode is usually in the kill wires and quite obvious.
Thses can be replaced for a few cents or the sub loom can be replaced for a lot of dollars .
The chip inside the magneto coil is neither repairable nor replaceable ( I have pulled a few apart ) .
So you test the coils by removing the kill wire
No spark with the kill wire removed = dead coil that has to be replaced

Click to expand...

Removed the kill wire to that cylinder and it's still not firing, so am assuming a dead coil - happily they're fairly cheap to replace.

Wurzel said:

Removed the kill wire to that cylinder and it's still not firing, so am assuming a dead coil - happily they're fairly cheap to replace.

Click to expand...

Yep stone dead
Now if the kill wires have diodes in them then test them as well lest they lead to a very short service life for the replacement coil.
And make sure you get the correct one or the engine will never run properly
Also test the kill wire for voltage
It is a ground wire so should only ever be ground ( engine off ) or open ( engine on )
A problem that had me going mad ended up being corrosion in the socket of a parking brake switch that allowed a tiny voltage to pass down the kill wire if you had your foot flat on the brake when cranking the engine, but not if the brake was on the latch.
That mower came back more times than a black fellas boomerang .

Wurzel said:

Removed the kill wire to that cylinder and it's still not firing, so am assuming a dead coil - happily they're fairly cheap to replace.

Click to expand...

TIP

Make sure you LOOK at the new coil. Some say UP and some other mounting tips on them. Summation, it is possible to mount one back to front or front to back depending on your coil.

She sure idles down nice with one dead cylinder (from your videos). You should of verified spark several pages ago. Get a cheap inline spark tester. Or just ground a plug out......

From all of this I think we've learned one thing and it goes back to what I always tell everyone when troubleshooting a mower...
Always start by making sure the machine is getting enough fuel especially on the no starts because well over 85% of the time that is the case..
After you have confirmed it is getting fuel or it's running, if a twin engine, always cancel out each cylinder to make sure it will run on both.
This is most easily done with a towel or a glove and popping the spark plug wires off one at a time with it running at a medium speed. No reason to have it going full speed but don't have it idling either.

In this situation this would have quickly determined that it was only running on one cylinder and we could have moved away from even talking about fuel for the time being.

Then, since you know it's a cylinder running issue, the next thing you do is check for spark and since you already have the plug out there's no reason not to put your finger in the hole and crank it over a few times just to see if it goes puff puff puff puff and blows your finger out of the hole with a regular pattern. It should never double puff or try to suck your finger in the hole forcefully.
If it does that you have some valve train issues.

So this would have quickly told us it's a spark related issue which leads us straight to the coil..

Then, as others have stated the way you check a coil before you ever take it off the machine is to pop the kill wire off it and then check for spark again..

Don't even bother with the ohm meter or other basic static bench tests because in the real world those are not accurate enough to spot anything but the most blatantly fried coil.

You need to see a good strong spark spark spark spark spark spark spark as you crank the engine over with no missing Sparks or no sitting there just barely moving around the tip of the spark plug or the insulator.

slomo said:

She sure idles down nice with one dead cylinder (from your videos). You should of verified spark several pages ago. Get a cheap inline spark tester. Or just ground a plug out......

Click to expand...

Yep - I certainly should have, I got distracted chasing down a fuel issue, I even have that tester...

Not being familiar with these engines I'd totally missed it was only running on one as well, had it been a four pot it would have been obvious. In any case, coil ordered, fingers crossed it works. Noted re orientation, the one I've taken off was clearly marked as such, will check on install of new one.

Wurzel said:

Yep - I certainly should have, I got distracted chasing down a fuel issue, I even have that tester...

Not being familiar with these engines I'd totally missed it was only running on one as well, had it been a four pot it would have been obvious. In any case, coil ordered, fingers crossed it works. Noted re orientation, the one I've taken off was clearly marked as such, will check on install of new one.

Click to expand...

Make sure your working coil can throw a good strong spark. Put that tester to work.

Wurzel said:

Hello All - am hoping the knowledge bank here may be able help. I'm resurrecting a John Deere LT166 lawn tractor with 16HP Briggs engine. It has sat for 2-3 years but was running fine, save for a snapped deck belt, previously. I've stripped and cleaned the carb and got it started, driving and mowing, but not very well. It basically won't run properly without choke. I've double checked the jets in the carb. I can just about get it to tick over without choke by adjusting the fuel screw, but it won't rev and it's obviously running far too rich. In any other position it won't even idle, or only for 10-15 secs before stuttering and dying. With choke it will rev, but is maybe at 30% power and clearly not running as it should. Oddly it can manage forwards, but reverse pretty much kills it.

Have I missed something on the Aisan carb? I thought maybe a fuel pump issue but if it runs at full revs, albeit it badly, it can't be? I've checked the tank cap breather as well. It has clean fuel, albeit mixed with whatever small amount of bad might have previously been in the tank, but I think it was bone dry. Is there a hidden jet anywhere on those carbs?

Thanks in advance...!

Click to expand...

Make sure you have good flow of fuel from the tank. A collapsed[internally] fuel line behaves in this manner.

Quick update - coil has arrived and is fitted but while it revs much better without choke, the problem remains, it will only take maybe 70% throttle. I've been a little short of time of late, but will get into valve clearances etc next.

Wurzel said:

Quick update - coil has arrived and is fitted but while it revs much better without choke, the problem remains, it will only take maybe 70% throttle. I've been a little short of time of late, but will get into valve clearances etc next.

Click to expand...

When you get time, change the plugs. A cheap long shot here. Rare but sometimes they get dropped or just fail.

Can you confirm now you have a strong spark on both cylinders?

but while it revs much better without choke, the problem remains, it will only take maybe 70% throttle.

????????????Give us a hint as to how it acts when it QUITS TAKING throttle.
Does it backfire, just hump up and start smothering like it wanting more gas through the carb or starving for gas.

Since that has a separate choke control what happens if you give it a part choke at 70% throttle????

Wurzel said:

Quick update - coil has arrived and is fitted but while it revs much better without choke, the problem remains, it will only take maybe 70% throttle. I've been a little short of time of late, but will get into valve clearances etc next.

Click to expand...

These things rarely have any valve adjustment issues that will prevent them from running or running just fine UNLESS someone has been in their monkeying around.
If you hear one popping out of the intake after it gets up to even slightly past a slow running speed then you can guess that the intake valve is adjusted to tight but that's because somebody messed with something.
These engines don't wear tight like car engine still.
When they wear and when they haven't been adjusted in their entire life etc you will find the clearances are three or four times what they should be but as long as you can get the engine to start and get past the correct compression release issue as it cranks, it will run just as perfectly as any other engine.
You would have to try to miss adjust the valves on one of these to cause a running issue or a specially a revving up engine issue.
The other valve train problems are not adjustment or wear issues at all but rather lack of proper assembly and safeguards when they're put together normally from a rocker arm stud loosening up and things getting out of whack with the angles or bending a push rod also.
The other common valve train issues are when a valve guide slips mainly from overheating because of grass and dirt and greasy grime build up on the cooling fans of the engine but in reality, more because it's a lousy design to begin with!
They pressed these guys into the heads so poorly and so loosely that a machinist and a machine shop who routinely sees car engine heads with just roll his eyes and shake his head at the poor setup.
They could have solved this problem over 20 years ago but they don't care because they don't mind when they fail and they don't mind selling replacement heads because that's the shops answer to everything is throw new parts at it.
I have NEVER replace the head due to a slipped valve guide but have fixed many.
They could have used several methods to fix this problem the easiest of which would probably have been to pin them.
But anyways, when this happens you'll get that pushrods and valve issues and usually a Pop-Pop here and there and then it won't start again.

I think you're going in the wrong direction worrying about the valves right now but I don't know if they've been adjusted properly before or not.

If it seems to only get up to 70% of proper operating speed and especially if it's leaning out like starving for fuel because it's either leaning out or it's bubbling and running extremely rich and coughing a little bit and maybe blowing a little bit of black.
Most commonly they starve for fuel though and this boils down to still a carburetor restriction in the jet.

I forget after all this time and comments if this is a walbro for a Nikki carb but after just saying this I remember it's a twin so it's not the same carb as the singles where on the Nikki people often put the jet in the wrong way I call it or at least the worst of the two ways you can install it and it often falls out and then the machine will run but excessively richly.
From but I remember you can also have the same problem with the jet falling out on one of the twin engine carbs.
One of the common one has two jets.

Regardless, to troubleshoot this now I would use my hand or a folded shop
cloth or microfiber towel to slightly restrict the airflow going into the carburetor as you try to rev It Up or even get a spray bottle with some gas in it or use some carb cleaner to slightly spray or even trickle a little bit of gas in there when you try to rev It up to see if by giving it more fuel it will rev up higher and smoother.
This is one way to confirm that you need more fuel and there is a restriction somewhere in the flow and the atomized mist getting through the carbon into the intake.

Also, have you cancelled out cylinders while this thing is running to make sure it will sit there and run on each cylinder independently?
This is very important because you could just have a very weak cylinder now not producing much power.

check fuel hoses to make sure they are not swelled up inside them.

Finally had some time to get to it this afternoon, have confirmed spark on both cylinders and also that it will run on either. I also made the governor / carb connection more permanent as it had been hooked over temporarily, which made me take a closer look at how it was working. I'm fairly certain the carb connection is OK, but I've no idea if the lower springs on the throttle cable are right - certainly the way it's connected at the moment mean it needs about 20% throttle before it starts moving the carb. There's a lot of slack in the mechanism due to how the springs are currently attached.

I'm wondering if the governor is somehow killing the engine at higher revs, it looks as though is opening the throttle way too much? If I partially cover the carb when it starts to splutter it recovers, as it would if I used choke to the same thing. It starts sucking really hard which is when it dies. If I gently manage the air going into the carb I can get it revving pretty hard, but left to it's own devices, the governor goes wide open and kills it.

I'm not sure re cause / effect here, but see video below:

Governor not killing it, starts to die - rpms get less - the governor opens throttle to bring rpms up. Issue not governor, it's .....

Wurzel said:

Finally had some time to get to it this afternoon, have confirmed spark on both cylinders and also that it will run on either. I also made the governor / carb connection more permanent as it had been hooked over temporarily, which made me take a closer look at how it was working. I'm fairly certain the carb connection is OK, but I've no idea if the lower springs on the throttle cable are right - certainly the way it's connected at the moment mean it needs about 20% throttle before it starts moving the carb. There's a lot of slack in the mechanism due to how the springs are currently attached.

I'm wondering if the governor is somehow killing the engine at higher revs, it looks as though is opening the throttle way too much? If I partially cover the carb when it starts to splutter it recovers, as it would if I used choke to the same thing. It starts sucking really hard which is when it dies. If I gently manage the air going into the carb I can get it revving pretty hard, but left to it's own devices, the governor goes wide open and kills it.

I'm not sure re cause / effect here, but see video below:

Click to expand...

It's not

Wurzel said:

Finally had some time to get to it this afternoon, have confirmed spark on both cylinders and also that it will run on either. I also made the governor / carb connection more permanent as it had been hooked over temporarily, which made me take a closer look at how it was working. I'm fairly certain the carb connection is OK, but I've no idea if the lower springs on the throttle cable are right - certainly the way it's connected at the moment mean it needs about 20% throttle before it starts moving the carb. There's a lot of slack in the mechanism due to how the springs are currently attached.

I'm wondering if the governor is somehow killing the engine at higher revs, it looks as though is opening the throttle way too much? If I partially cover the carb when it starts to splutter it recovers, as it would if I used choke to the same thing. It starts sucking really hard which is when it dies. If I gently manage the air going into the carb I can get it revving pretty hard, but left to it's own devices, the governor goes wide open and kills it.

I'm not sure re cause / effect here, but see video below:

Click to expand...

It's not the governor. The governor is doing its job and when the engine starts to slow down RPMs it opens up to try to maintain the speed which eventually and pretty quickly in this case it opens to full throttle trying to get more speed.
It can't do that because there's not enough gas flowing through somewhere..
That's why when you use your hand your accomplishing two things. Firstly, you are blocking off the airflow and restricting how much air goes in so that Richard's whatever mixture is in there and secondly after that brief second it probably allows a little bit more suction through the jet because obviously some gas is going through so it does get a little bit more fuel flow but overall you're not getting enough fuel flow on its own.
If you stood there with a spray bottle of gas or carb cleaner and tried to rev it up and gave it a little trickle of extra fuel source you could also get it to speed up smoothly without bogging.
What's happening, it looks like to me, is the governor is opening and the throttle is going to wide open and it doesn't have nearly enough fuel so it just bogs and starts to die.
I forget all the previous discussion but that carburetor looks pretty simple like you remove the bowl and they will be a jet screwed into the side of the center section of the carb or maybe it's got one of the jets screwed up into the bottom of it into the middle.
Those have to be removed with a skinny screwdriver that just fits The notches in the brass jet.
It sounds to me like a simple main jet is partially restricted

You need to put the air shroud back on that engine. (before you overheat and ruin the engine. The air shroud no longer needs to be off.

Have you had the main jet out of that carb? (and the emulsion tube that is normally connected to the main jet?
If so, did you look at the emulsion tube carefully and rod out all the itty bitty cross drilled holes in the emulsion tube????Some are really small and hard to see if the tube is dull colored.
Does the engine set and idle good and smooth?

We can get into the static governor adjustments later.
It's still starving for fuel or getting too much air. (due to a leaking intake manifold behind the carb. Have you had the manifold off and installed/checked new seals where the manifold bolt to the heads and make sure the plastic manifold is not cracked???
In your post number 18 that gasket is bad and also appears to be installed wrong between the carb and the intake? Have you replaced that gasket and did you get it installed correctly?

Yes the main jet and emulsion tube above have been out a few times and thoroughly checked, including the cross drilled holes in the tube body. I can't find any leak around any manifold mating surfaces or seams by using carb cleaner. I will swap the gaskets between carb / manifold adapter / manifold for good measure. Is either a case of too little fuel or too much air, there's nothing to say the main jet is original, but it's clutching at straws. I also changed the fuel lines between filter / pump and valve cover / pump as they had surface cracks. Engine does settle into a steady idle and doesn't hang. The only thing I haven't tried is giving it some ether at the carb when it starts to stumble, the result is predictable but I'll confirm nonetheless.

Wurzel said:

Yes the main jet and emulsion tube above have been out a few times and thoroughly checked, including the cross drilled holes in the tube body. I can't find any leak around any manifold mating surfaces or seams by using carb cleaner. I will swap the gaskets between carb / manifold adapter / manifold for good measure. Is either a case of too little fuel or too much air, there's nothing to say the main jet is original, but it's clutching at straws. I also changed the fuel lines between filter / pump and valve cover / pump as they had surface cracks. Engine does settle into a steady idle and doesn't hang. The only thing I haven't tried is giving it some ether at the carb when it starts to stumble, the result is predictable but I'll confirm nonetheless.

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I am certain you're going to find if you give it some extra fuel, I would use gas and a spray bottle or card cleaner and not starting fluid because that's way hard on an...that you will find it will not lean out like that and keep the throttle plate wide open and start to die.
I can see in the video that the throttle is going from the minimum idle setting all the way to wide open from the governor as soon as it runs out of fuel.

So if it's not the jet clogged up or way too small of a jet opening from being the wrong jet which I doubt is the case but it is possible, my next thought would be not enough fuel in the bowl.

This doesn't happen very often but it certainly can.
It can be from the fuel pump or fuel lines not supply enough fuel like what I fuel line degrades inside and swells up and pinches itself off so instead of being a nice flow it's just a trickle.

I think the fastest way to test this in your case would be to remove the fuel line from the carb and not do the normal crank the engine or run it over and watch it spurt out of the line for the fuel pump which that would be something I would still probably do but I would go ahead and get a new piece of short fuel line and a small gas tank or some other way to provide fuel to it and just hold that tank in your hand as gravity fed and then let it run to see if it runs normally or still does the exact same thing.

If it acts the same way then I would suspect the inlet valve of the carburetor.
I think that carburetor will have the needle valve with the rubber tip and those don't usually cause restrictions but the push mower style Briggs with the rubber seats up inside the hole like the Tecumseh often swell up and the hole gets so small they only trickle when they should flow much greater.
And either way, there can also be something clogging it up as I found three brand new Chinese engines on riders and just two seasons that had some sort of cloth wadding packed into that inlet from the fuel line that was restricting flow greatly.

If a gravity fed plentiful fuel source doesn't straighten it out for test purposes I would remove the bowl, float and needle valve and blow a strong air pressure backwards through the needle valve letting it blow the air out of the carburetor fuel line inlet nipple.
I have had some so bad I've had to run a wire or a pipe cleaner through that passageway.

I just think you have to be leaning out and starving for fuel and these are the most common ways that happens.
Some other rare occasions are when the float is wrong or something is rubbing inside and it can't move freely or far enough.

Right:
AS TobyU says bypass the existing pump fuel system by rigging up a gravity feed tank.

If you do not have a tank as such:
I have as a quick bypass of existing fuel systems is rig up a vertical piece of 1/4 inch or 5/16 tubing about 3 ft long, (tire the fuel so it will stand up vertically as gravity feed to the carb take a small funnel and fill the tubing with gas, then start the engine and go to full throttle immediately. The engine should run good for about 60 sec or more just using the gas in the tubing plus the full bowl of the carb gas.
If that works ok, think about getting a regular USA LMT carb or even roll the dice and install a clone nikki. Your carb and governor linkages will have to re-arranged. to the USA style but rhose can even be made using survey flag wire. (your existing LMT carb and linkages linkages are of the un-usuall type is mainly why you are stuck for now with that carb and we do not know for sure if it's the carb, but all now is pointing to a carb that is leaning out for some reason????????????

Thanks both. We have previously tested for good flow at the carb inlet, but not the passage between the inlet and bowl / main jet. I've had the float valve apart but can't recall what tip it has or what it seats in. I'm pretty sure I blew it all through previously in the initial carb cleans, but there could still be a restriction there. In any case I'll do it again and also with a temp fuel supply which I can rig up fairly easily.

Just curious.
Are you located in the USA?

The reason I ask is you say that carb is Asian and that is not a standard Walbro LMT throttle and choke linkage set-up is not normal for a USA Briggs twin?
(Some of that re-branded equipment (has a JD name but parts and pieces made by others for JD) has some strange rigging sometimes. Frankenstein type equipment maybe)

Forest#2 said:

Just curious.
Are you located in the USA?

The reason I ask is you say that carb is Asian and that is not a standard Walbro LMT throttle and choke linkage set-up is not normal for a USA Briggs twin?
(Some of that re-branded equipment (has a JD name but parts and pieces made by others for JD) has some strange rigging sometimes. Frankenstein type equipment maybe)

Click to expand...

I couldn't see much of the engine in the video but it kind of looks like one of the older horizontally opposed twins to me.
I think I could see an aluminum crossover intake.

Forest#2 said:

Just curious.
Are you located in the USA?

The reason I ask is you say that carb is Asian and that is not a standard Walbro LMT throttle and choke linkage set-up is not normal for a USA Briggs twin?
(Some of that re-branded equipment (has a JD name but parts and pieces made by others for JD) has some strange rigging sometimes. Frankenstein type equipment maybe)

Click to expand...

UK, note its an 'Aisan' not 'Asian' carb

TobyU said:

I couldn't see much of the engine in the video but it kind of looks like one of the older horizontally opposed twins to me.
I think I could see an aluminum crossover intake.

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Yes aluminium crossover intake

Governor is working as normal. Move along. Your video shows it clear as day.

Looks like the pilot circuit runs out of fuel and hits on the governor for more gas from the main jet. Indicates fuel delivery issue and or clogged carb. Vacuum leaks??????

Dump fuel tank out and flush with fresh fuel. Make sure the tank inside is spotless. All new fuel lines from tank to carb.

Pull fuel hose off at carb inlet. Should drain the tank with a solid flow AT the carb. Drain gas into a glass jar. Pour back in the tank through a coffee filter.

No reason to be on 8 pages now and still have a hunting/surging engine. OP has missed something or ignored/missed some advice.

Cleaned debris & grass from fuel tank, ran carb through ultra sonic cleaner 3 times, blew lines & carb. Did it again, blowing again back, sediment bowl & HEY, out comes another blade of grass!!! So, yes,
possible something missed. Engine ran 10 to 20 minuets & popped - died. Silly blade of grass!! If 1st don't succeed, try try again, don't go off course chasing something else.

STEVES said:

Cleaned debris & grass from fuel tank, ran carb through ultra sonic cleaner 3 times, blew lines & carb. Did it again, blowing again back, sediment bowl & HEY, out comes another blade of grass!!! So, yes,
possible something missed. Engine ran 10 to 20 minuets & popped - died. Silly blade of grass!! If 1st don't succeed, try try again, don't go off course chasing something else.

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OP has 2 accounts.

Thanks for letting us know.

Few pages back you said you see a welch plug leaking air.
How did you re-seal the welch plug? (plugs)


It appears maybe that carb has a 3 piece High speed main jet area, emulsion tube, Main jet and a high speed adjustable H jet in the bottom of the bowl.
Post up some pictures of these 3 pieces showing the tip of the H jet.

Forest#2 said:

Few pages back you said you see a welch plug leaking air.
How did you re-seal the welch plug? (plugs)

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Jumping in here, Briggs recommends clear nail polish to seal welch plugs.

slomo said:

Jumping in here, Briggs recommends clear nail polish to seal welch plugs.

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The reason I asked is he said in a previous post few pages back he placed his finger over a leaking welch plug and it made no difference. (so he just moved on)

He needs to re-check/re-seal the welch plugs especially after using high pressure compressed air into the carb.

I sealed the welch plug up with a cap of glue as temporary measure, I'm certain it was now airtight.

@Forest#2 you mention a high speed adjustble jet, which are you referring to? The one in the bottom of the bowl (254 below), I undertood to just be a drain plug, certainly loosening it means fuel leaks from the perpendicular drain hole it covers. If the high speed is adjustable, that would seem a very obvious thing to look at.



I've put the carb into boil again and attach photos of the main jet, emulsion tube and the screw marked 254 above. Once back together I'll hook up to a temporary supply to see if there's a difference.

Meanwhile the float jet and it's seat are clean and flowing freely.

I haven't yet drained the tank and refilled it through a coffee filter, if the temporary fuel supply yields a different result, I will.

I've also included a photo of the air side showing the internal ports in the body, again all cleaned and flowing with carb cleaner, but as I've said previously, there are passageways on top that I can get carb cleaner through, but can't see through or wire through.

As I've said before, I appreciate your help here and yes, it's quite possible I may have missed something. but this issue is deeply frustrating and I am not ignoring advice. I'm not a mechanic, so am acting on the advice given to the best of my ability.

Yes, that is just a bowl drain. #254
Your High speed jet is the one that screws into the side of the carb in your picture 2.
When you put the carb/bowl back on the carb the area below this jet to the bottom of the bowl has to be sealed good when the bowl is installed or gas will bypass this main high speed jet (at the bottom of the bowl) and the engine will run too rich. Make sure this jet and it's passage ways are clear/clean.
This is the High speed gas feed source for the bottom of the emulsion tube.

Just couple hints. I've never seen that exact carb but couple hints to check.
You need to remove that high speed jet that is in picture 2 and carefully look behind it to see if their are any type of passages other than straight thru.
Most are just straight through to feed the lower portion of the emulsion tube but that one for some reason has a thick casting it screws into.
Some others that jet screws into a thin casting on the side and it has to be removed BEFORE the emulsion tube can be removed on those type carbs.
Also the little slot that is ABOVE the throttle plate needs to be closely inspected and make sure it's not distorted or restricted because as the throttle opens for high speed addition air across it is what draws additional fuel through the H jet up through the emulsion tube.
The upper ring portion of the emulsion tube must seal at it ring to prevent a rich bypass of fuel check the upper portion where the tube fits in the carb's body casting and make sure the lower screw portion is holding the emulsion tube securely seated in the carb body for sealing at each end.
You have to be careful removing that jet and also re-installing. Some require a good snug fitting Hollow ground screwdriver to keep from distorting or breaking the side and also be careful re-installing and not cross thread. some have a slight taper thread and do not re-start easily and some will also get snug before they bottom so keep a heads up about such.

Forest#2 said:

Just couple hints. I've never seen that exact carb but couple hints to check.
You need to remove that high speed jet that is in picture 2 and carefully look behind it to see if their are any type of passages other than straight thru.
Most are just straight through to feed the lower portion of the emulsion tube but that one for some reason has a thick casting it screws into.
Some others that jet screws into a thin casting on the side and it has to be removed BEFORE the emulsion tube can be removed on those type carbs.
Also the little slot that is ABOVE the throttle plate needs to be closely inspected and make sure it's not distorted or restricted because as the throttle opens for high speed addition air across it is what draws additional fuel through the H jet up through the emulsion tube.
The upper ring portion of the emulsion tube must seal at it ring to prevent a rich bypass of fuel check the upper portion where the tube fits in the carb's body casting and make sure the lower screw portion is holding the emulsion tube securely seated in the carb body for sealing at each end.
You have to be careful removing that jet and also re-installing. Some require a good snug fitting Hollow ground screwdriver to keep from distorting or breaking the side and also be careful re-installing and not cross thread. some have a slight taper thread and do not re-start easily and some will also get snug before they bottom so keep a heads up about such.

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I've removed that jet numerous times and checked clear, but maybe there's some type of restrictive build up I've missed. I think it is just the straight passage from memory, but I'll check; also emulsion tube seating.

Boiled carb and back on, temporary fuel supply didn't change the condition.

Spraying a mist of fuel into the carb did allow it to rev when it started stumbling at the usual 50 - 75% revs.

Time is precious and this has used too much of everyones, so meanwhile I'm seeing if I can find a returnable Chinese carb from Amazon in the hope it fits and works.

Symptoms of starving for fuel.

That carb has had water inside it. See that green corrosion on the needle? Looks to me that needle might not travel up and down proper. You need to clean all those parts in CLR or similar. Remove all that corrosion.

Outside of the carb is filthy too. You said you boiled it clean? It's filthy. Might be an air opening of some kind caked up with oil and grass not allowing the carb to breathe.

You've missed something I feel. We are at 10 pages now and the thing still has issues.

That carb will need a CLR bath if it will even come clean. Carbs like those (corroded) are tough to get going again.

As slomo says:

That green corrosion not coming clean from your boiling and cleaning is also a clue that the passages inside are not getting clean plus the outside of the carb is not even cleaning itself.
That green gunk has most likely hardened inside a small orifice and restricting a passage.

If the CLR don't get it loosened up eventually try a 50/50 mix of vinegar and warm water, soak the carb for 30 min's, send some air through the passages and the outside surfaces, brush the carb with a stiff paint brush or toothbrush, then back into the warm mix for about 45 min's, rinse again, blow dry the passages, and as a final add a spoonful of baking soda to water and brush and rinse the carb good. You can gently clean the needle with the tooth brush and a cleaner. do not get aggressive with the vitron tip.
I suspect ethanol gas has went bad inside that carb, seeing the blue corrosion everywhere on the internals.

Vinegar is a acid and if not neutralized with baking soda it will keep chewing on the magnesium/aluminum and the carb will feel greasy and turn black. No major harm but just do the neutralize thing.

The 50/50 mix of white vinegar and water will not harm the carb, I use it in Ultrasonic tanks for carbs and sometimes have to make several runs in heated vinegar/water mix when I get into one like yours and I mainly use the baking soda rinse to eventually stop the acid reaction on the external body of the carb causing it to change color and remove the greasy feel.
What it really needs is a good UltraSonic cleaning.
The linkages on them Amazon clone carbs is going to be wrong for your throttle and choke. Only thing a cheap one would be good for is to just bolt on and operate the throttle manually so as to see if you get a good run on the engine manually operating the choke and throttle. You need to check your bolt on spacing width and the size of the carb throat opening. These dimensions are sometimes listed when looking at pictures of carb part numbers on fleece bay then go elsewhere in your vicinity to maybe find that same carb.

Yes I should mention external photos were taken pre-boil. Its cleaned up the outside well enough but will need the acid / salt or acid / baking soda mix to sort the green, CLR eats brass from what I see.

I've found one Chinese one with horizontal throttle and choke plates and what looks to be the right bolt pattern, but it'll take a few weeks to get here and is still a gamble, also no mixture adjustment or anything on it.



It would be far better to get this one working - the fault has been completely consistent all the way through, even when it was on one cylinder, so I feel sure the fault is closely related or in something already covered.

Maybe try what is it citric acid??? Mercedes Benz people use it to flush out radiators and such. Works but is gentle. Maybe Bert can chime in here with some help. Do some research on it.

Well more cleaning with particular attention on the main jet, reaming through with some old wound guitar strings and I think while it looked clear before, there may have still been a slight restriction, is certainly revving better now. Also put more high pressure air through everything again which may have moved something. It's still hunting a bit at high revs, but way better than before.

Thanks again for everybody's help, have learnt a lot and delighted to get it back into usable order.

I noticed in your last pictures that it appears that the Low idle jet still has the plastic limiter adjust cap on it even though you got it removed.

If it's not adjusting for a good smooth low idle you might have to remove the plastic limiter to get a full adjust. Do not try to break the plastic off or you might break the jet. Take a Dremel tool and grind the plastic off. Sometimes when the plastic limiter comes off you will have to use the dremel tool and slot the metal top of the jet for a small screwdriver.
I've seen some carbs that just a 1/4 inch turn of the l jet would greatly improve/reduce high rpm hunt or slight roughness but the 1/4 turn would still give a good low smooth idle. (this tweaking is done with a warmed up engine and the breather installed) Do not tweak/fine adjust when cold engine)
Also sometimes a high speed slight hunt will quit when the mower deck is en-gauged and a load is placed on the engine.

I'm assuming that the governor is adjusted properly and their is no slop/slack in the throttle linkages.