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I've got a pair of Quantum 5hp mowers, both on 20" mulching decks.
The one will start and run fine for about 20 minutes, then it starts acting like its running out of fuel, then it dies.
If I pump the primer three times, it starts right back up and goes for another few minutes, it'll repeat that die/restart behavior as long as you care to keep restarting it.
I've had the carb apart, even swapped it with another identical engine. The fuel line is new, the tank is spotless clean, (Even swapped that with the other mower).
I eliminated the kill wire and switch, which is the only kill circuit its got.
I've even swapped the coil and flywheel from the other mower but it persists.
I went so far as to pulling the head off after it stalled for the 8th time the other day to make sure the valves weren't hanging up but they're seated tight at TDC.
Judging by the look of the bore, its got a lot of life left in it. When it runs, it runs fine and cuts fine, but once it starts stalling, it keeps it up over and over till it sits overnight.
The gas is fresh, I replaced, then swapped the gas cap with the other one, and no change. The other one runs perfect and will run all day but that one has a lot more use on it now.
This started about two years ago, and I put it away to deal with later. I dug it out the other day, and started trying to troubleshoot it but have gotten no where.
When it dies, it acts like its running out of fuel, it starts running bad, surges a bit, then shuts off. I have to prime it like a cold start to get it to restart, but it fires up on the second pull every time but dies after another few minutes, and I have to keep repeating the same thing. It acts like it stops feeding fuel after about 20 minutes, but after it stalls, the fuel bowl if full. I replaced the float, needle, and cleaned the carb but it didn't change a thing. Then swapping the carb and fuel tank should have proved out both parts, as they don't act up on the other mower and the other parts do the same on this one.
Cold the valves have about .005", hot they go to about .002". So they're not hanging open. Besides, if they were, it wouldn't start right back up so easy. The motor doesn't get 'tight' and its got good compression. I does seem to run hotter than the other one but not enough to say its overheating.

It runs too long to be a mixture issue or vacuum leak, it also runs too long for it to be heat related. I generally get 3/4 of the way done mowing the yard before it acts up. I've owned this one since new in 1990.
(Motor # 122702 3131-01 90022129). The second mower was bought used a few years ago as a back up, but its always puffed a bit of oil smoke and used some oil. Its likely got far more time on it then the one with the running issues.
Time wise it really acts like a tank not venting but I've both swapped the caps and left the cap loose as well with no change. And it dies faster the second time and each time its restarted after that. Filling the tank makes it margninally better after the first time it dies but not enough to say fuel level has much to do with it. A full tank would last me four cuttings in my yard.

Just about the only thing you have not swapped over is the long induction tube.
They tend to get cracks on the under side from heat ( thermo set plastic ).
Usually it will surge .
Some are alloy which do get hot & leak big time .

I already swapped the intake tube with the good mower, it made no change. The other mower still runs fine and this one still dies after 20 minutes.
It definitely seems like its running out of fuel, hitting the primer button three times gets it started again every time but the run time is less with every restart, eventually getting to the point where it won't go more than a few feet without dying.
I thought at first there was something floating in the tank because it seemed to begin acting up when I stopped the mower when going forward. As if there were some water or something that was getting drawn in as I stopped the mower, and shaking the thing back and forth seemed to stop it from stalling when it began to act up but eventually nothing helps it. The tank has been off, washed out with fresh gas, and even swapped with the other mower but nothing changed.
The carb bowl shows nothing. I did check today when it stalled for the 11th time, if there was fuel in the bowl, and I found if I unscrewed the bottom jet, fuel flowed steady, so its not out of fuel, and the needle and seat are working. Yet it won't restart unless I pump the primer as if its a cold start every time. It only resets and runs fine if its cold or has sat for a few hours. Then it starts all over again. When it first starts, and is warmed up, it runs perfect, but only for about half the lawn, or about 10 80ft rows or so back and forth. It starts to act up the same way and at the same point every time.

This mower has a fixed throttle, the plate is bent and locked at full speed. The only control is the blade brake and primer bulb.
It never surges or runs rough, it just goes right into the stumble then stall behavior.
When it dies and gets really bad, after a dozen or so restarts, at the point where it will only start and stall, if I spray carb cleaner down the carb throat I can keep it alive, so its definitely not moving fuel when it happens, but the fuel bowl is full.

I pulled the intake and gave it a really good look and no cracks, the carb oring is fine, and the gas is fresh, and the same gas I run in the other mower. If it were dirt in the carb or tank, I doubt it would die in the exact same place or time every time I mow the lawn.
It begins at a point where I sort of push the mower down a slight grade at the end of a couple rows, when I push it down and stop, that's when it begins, and from there it progresses till it won't stay running.
The second mower will run all day, even with parts swapped off this mower.

Remove blower cover. Clean the engine block cooling fins all the way around the cylinder. Any dirt or oil, REMOVE it.

Spray some flammable wonder juice, looking for vacuum leaks around carb and intake pipe.

Either the coil is getting hot or the fuel is percolating like back in the old 350 Chevy days (not likely). Get an inline spark tester. Watch it at the 19 and 20 minute mark. See what you got for spark when it dies on you. Harbor Freight is your friend.

Air, fuel, spark and compression.

slomo

Loosen the gas cap the next time it happens, leave it loose, and see if that solves the problem. If it does, vent on the cap is plugged, replace the cap.

Thought he did the gas cap trick? Maybe not for 20 minutes? Like Rivets said, leave the sucker wide open and see what you got.

slomo

If it stops dead like it has been turned off , then that is what is happening, it is turning off
Only a couple of things that can cause this
1) faulty coil
2) faulty kill switch
3) faulty kill wiring
4) faulty high tension lead
On fixed throttle machines with a flywheel brake I have found the switch to be he problem.
Usually the mounting actually gets hot then allows the switch to move just enough to shut down the engine.

The requirement for priming the carb could be a lot of things.
Some engines just require a prime hot or cold and some don't.
All depends upon the effiency of the idle circuit in the carb , float level , valve lash , piston ring wear etc etc etc

I tried a few things on Sat. I tried running it with the cap loose, (had to put a bit of tape on the cap so it didn't vibrate off). No change, it died at the same point.
I bought a new coil, set the gap at .010" and gave that a try, no change, it died at the same point.
I've already swapped the intake pipe out and looked it over for cracks, I even wiped it down with RTV figuring if there were any cracks hiding they'd be sealed, or at least it would change something but it does the same thing.
When it dies, it acts like its running out of gas, it happens at the point where I mow one corner of the yard, where I'm pushing the mower back an forth to get to the edge of the lawn that borders the neighbors hedge row. Regardless of which way I mow, that section ends up at about the half way point time wise.
When it dies it starts surging a bit, then it sounds like its about to stall but it'll sputter along for a bit before it finally dies out completely. Sometimes if I stop, and shake the thing a bit it'll smooth out and keep going but never for more than a few seconds.
Loosening the cap, pushing the primer bulb, tilting or shaking it won't help once it gets to that point, it dies out and it'll take three or four pulls and 3 pumps of the primer to restart it. It'll restart and run fine for a couple more passes and repeat the same thing. The longest I've gotten it to keep it up is 11 restarts, then it won't run no matter what I do. By the time I push it back to the shed to check for spark or fuel, its already able to start on its own again. Since it starts back up, I doubt if its spark, (I have an inline spark tester but its hard to see on a bright sunny day, and if it were spark, its cured itself by the time I walk it back to the garage or shed.

If I push it till it won't stay restarted, spraying carb cleaner into the carb won't get it running. All it does is make the eventual restart harder and give me a ton of black smoke.
When it dies, there's no black smoke, so its not flooding out.
The kill wire is removed from the coil, it has been since this started. If I need to kill the engine I just pull the plug wire or wait a few minutes and it'll die out on its own.
I've swapped in the following new or 'known good' parts off another perfect running mower:

• Coil, tried two used one's and now a brand new one (New style p/n 590454)
• I drained and flushed the fuel tank, no change, so I swapped it with the other mower, still no change.
• Carburetor, cleaned it first, it didn't help, so I swapped it with the other mower.
• Intake tube, removed it, changed the gasket, then swapped it with another mower, then coated it just in case, no change
• New spark plug, then went back to a known good one from the other mower, no change. (Briggs 5095K, or Champion RJ19LM)
• New air cleaner,
• Checked and swapped out the gas cap, no change. (B&S p/n 691034)
• Checked the flywheel, swapped it with the other mower. Key way was fine.
• Checked valve clearance, valves are not open or 'tight' when it stalls.
• Fins are clean, its been apart 30 times now, but it does seem to be 'hotter' than the other mower when this happens and it stays hot longer.
• Oil is clean and fresh, (SAE 30 non detergent).
• New fuel hose, 1/4" ethanol resistant black fuel hose.
• Hot valve clearance is Exhaust - .003", Intake .004, cold is Exhaust .010" Intake .008"
• Compression feels the same hot or cold, the motor doesn't feel 'tight' and it don't rattle or knock when hot.

I've had the head off this thing, the cylinder looks like new, the head has minimal carbon on it, and the valve guides feel fine.
The exhaust valve looked like its been super hot, lots of blue heat swirls and a hardened white top surface. The intake was just black, the ports are clean. The muffler is clear, I've even swapped that and run it with a plain old tube type muffler just to see if opening up the exhaust helped anything, but it didn't. It just make it louder.

When its running and not acting up, its hard to kill, I can push it through heavy grass as fast as I want, once it acts up, it'll stall super easy.

Sunday morning I drained the fuel tank, drained the fuel bowl, went and got a fresh batch of gas, treated it with Sea Foam as I always do, and filled the tank. I started it up for the first time that day and let it run, (the throttle is fixed, no choice on the RPM), it was running at or around 2,900 rpm using a contact type tachometer
I let it sit there on the trailer and run till it ran out of gas, it ran fine for 3 hours and 4 minutes without any signs of stalling. I refilled the tank and tried to mow some grass, and it stalled in less than a minute, I'd restart it, and get another 30ft or so, it kept that up till it wouldn't restart again.
I put it back up on the trailer, tank still full, pumped the primer 5 or 6 times and restarted it, and let it run, it ran there with the blade brake tied back for another 2 hours and 10 minutes before running out of fuel.
Movement definitely affects it. It seems like it'll run fine if run with no load and no movement.
I refilled the tank, restarted it, and again it stalled even as I pushed it down the ramp off the trailer.
It did the same thing, once hot, if I move it or put a load on it it dies. If I let it sit, it runs for ever.
The fuel is fresh, I just had the fuel bowl off and rechecked the jet, and there's nothing floating around, the kill wire is not on the coil, and I even taped over the terminal just in case.

Meanwhile, its twin, an identical mower, runs fine with all of the original parts off this mower that I swapped from the bad one. The only thing I've not 'swapped' is the short block, deck, and shroud. At this point, the blade brake is removed completely, as is the switch as well.
I don't know if it matters or not, but something I did try with it running was to start it with the drill, run it without the shroud on it, and I poured water over the oil to see if it had a bad lead but I can turn the hose on it and it won't die when wet. I can wiggle and move the plug wire around and can't make it stall. From the start, I felt its running out of gas, it acts like its running out of gas or got water in the fuel when it acts up, but all that's been checked and proven. The carb is off the other mower, if I swap it back, the other mower still runs fine. I've gone so far to swap the coil, carb, intake pipe, tank, and spark plug all at the same time from the hot mower to the other mower and there's no change, once it acts up, it keeps it up till its cold again. Regardless of the parts bolted on it. When its cold, it starts with three pulls every time. I pump the bulb three times, pull the rope twice, it starts on the second pull, then stalls, I prime it three more times and its off and running. Both do the same thing and have since brand new. When the bad one is hot, it takes a three to five more pulls to get it going after it dies.
Once it sputters, there's no stopping it from eventually dying. I can't just stop, and let it run, its going to die no matter what. I tried just letting it run after the first restart, not moving it or putting a load on it but it dies just the same as if I was mowing grass. Yet if I let it run untouched from dead cold it'll run till the tank is empty every time.
I'm getting close to the point of just taking my shotgun to it and solving the problem once and for all but I'd really like to know what on earth is causing this before I blast it to bits or waste a couple good slugs on it.

u know way more about this stuff then i but i have been watching ur post hoping to c a success story . not sure if u tried cyl comp. test cold vs stall temp ? did u rotate engine while hot with valve ( is it ohv ?) cover off ? maybe a spring is weak . i know it doesnt explain running well at idle but who knows ! good luck hope u solve it

I haven't put a compression gauge on it but really didn't see the need since it doesn't feel like its lacking any compression.
I did check the valve clearance and guides, both hot and cold and there's nothing I see wrong or different from the other mower.
The clearances vary a lot with heat, but I'd say thats normal. The valve tappet clearance gets tighter when it warms up but it don't go to zero, so the valves are not hanging up. With the motor hot, and to the point it won't stay running, I zipped off the head and checked the valves and at TDC, both are seated tightly.

The thing that gets me is that it will run fine if left sit. There's no idle or full speed, the speed is fixed by the throttle bracket. There's no throttle, just a safety handle and blade brake, and the primer bulb. No other controls on this mower. I did try bending the tab up on these to add a manual throttle control but neither one will 'idle'. They shut off dead below full throttle. Its all or nothing. There's no kill wire or switch on the throttle plate, only on the blade brake, and that's now removed till I fix this. I have a similar mower, a slightly older 4.5hp Quantum that also runs fine, but that one has a throttle control and different primer bulb location. Its got a kill switch on the blade brake and throttle plate.

The two identical mowers are both older Troy Bilt mulching mowers with the rear bag option.
I've been trying to keep these going because I like how fine they mulch the grass, plus they're super light to push with handles suitable for my height. The third one has a real low handle set up on it and is super uncomfortable to use. The deck is also super flexible on that mower. These two Troy Bilt decks are very solid and they never rusted.

What I may do is just toss the Quantum motor and put an older style motor on there. I've got a good running 3.5hp I took off an old rusted out deck that will fit that deck. That one runs perfect.

I actually had a third one of those Troy Bilt mowers with the 5hp Quantum motor on it, that one died early on, it was mowing just fine and it suddenly lost power and died. When I tried to restart it I could hear something rattling inside. The piston is moving, so I figured it must of broke the came or governor inside. I just put it on the shelf and stuck a used Honda GX motor on it I had trash picked. It still runs but its at my other house, the Honda runs good but has cost me a dozen spark plugs and a couple of coils over the years.

My John Deere did the same. I found some kid had put things in gas tank that vibrated to stop up the gas intake in the tank. It would start fine and then just stop some time later 15- 20 minutes. Next time it would start ok.

You've swapped everything but the deck paint.

My guess was the idle screw is set wrong at 2900rpm and the gov-na' slash throttle spring/s are not working proper. Summation, carb linkages and springs are a foul. But you've swapped carbs and everything else fuel related.... Still sounds like a dirty fuel tank or collapsing fuel line. This might be dumb but the fuel tank is higher than the carb? You mentioned it's better on a full tank.

You've removed the ignition coil kill wire completely right? Engine should run till the tank is dry. Next guess is clean/sand/polish to bare metal, ignition coil mounting pads, same coil mounting area and mounting screws. Again you've swapped coils. Thinking block was getting hot and expanding slash moving around breaking ground from the ignition coil. Shot in the dark.....

Are the cylinder or head missing cooling fins? You said they are all clean. As in you can see clean aluminum all around the cylinder and head?

Do a compression and leak down if possible. Something is getting hot and out of tolerance. But it will run for 3 hours on flat ground.

Still sounds like fuel. Back to the basics, air, fuel, spark and compression.

What else, that has remained ON the engine that hasn't been swapped?

slomo

Just reread this entire thread and something caught my eye. Your differences in valve clearances, hot vs. cold, are contributing to the problem. When they are hot they will not open enough to get the proper amount of fuel into the cylinder. That amount of difference is most likely caused by overheating. I’m assuming that you have made sure that the cooling fins are clean, so that air can circulate past the flywheel, over the cooling fins, and out either over the head or under the cylinder. Many, many years ago a student had an engine that would quit after it warmed up, where we found that the exhaust valve would actually stretch. We thought that the guide clearance was two small causing friction, so we rebored to specs. Ran a little longer but problem still occurred. We then replaced the valve and that solved the problem. Never saw this occur since, but I thought I would throw it out there. What do the other tech here think, possibility??? Or is my age showing??

I too noticed the gap issue, didn't add up. We don't know how long the cooling process was in between checks. 5-10 minutes could cause a couple thou I would guess being off????

Being that he's replaced everything else and the EX valve is cheap, sure, replace the little guy. I would change both while I was at it. Sounds like it runs good other than the unexplained shutdowns.

Honestly I was thinking something internal but didn't post for fear of getting trampled on by you real pros. LOL Rivets called it though, full credit to him. I've never seen it so didn't post about it.

slomo

Valve clearance changes between hot and cold are normal. On most engines, if set cold, they're set a bit loose because the gap will tighten up as things expand with heat. I'd only be worried if the clearance was zero, which would mean a valve wasn't able to close. That's not the case. Besides, it'll run through a full tank of fuel at about 3,200 rpm without any stalling, it only stalls when its mowing grass, or being pushed or pulled around.
The carb has been gone through 10 times now, plus I've since swapped it with the other mower, and the carb off this one ran fine on the other mower. As did all the other parts, including the fuel tank.
The fins are clear, the motor is clean top to bottom and its not missing any fins.
I did clean the coil posts and the coil is new, and has been swapped back and forth twice now.
It does seem to run hotter than the other mower just like it.
I check the compression with a thread in gauge cold and got 87 psi, and got 91 psi hot.
I checked the other mower for comparison, and got 79 psi cold, and 88 psi hot.
Each time I pulled the rope till the gauge stopped gaining compression with the carb wide open.

It definitely acts like a fuel problem but I've swapped everything fuel and spark related and the problem didn't change.
I pulled the head to check the headgasket and valves after it seemed to get hotter than I thought it should but there's no cylinder damage, the valves weren't too tight, and the head gasket wasn't blown.
The point where it always seems to act up first is along one side of the lawn. These properties are each slightly higher than the next. It seems to be when the mower is leaning forward a bit or when I stop it pushing it back and forth around obstacles. That made me think there was something in the tank or carb bowl, but I've been over that a dozen times now and the tank is clean, and the carb runs perfect on the other mower. Yet when it dies, after a handful or restarts and finally won't restart, it won't fire up on carb cleaner shot in the carb. But 10 minutes later it will start and die a few more times. But it won't be ready to run any length of time until its cold again.
Something I did try today was to swap out a completely different carb, off a similar engine but not its twin. That mower had a throttle cable and movable throttle plate. What I found was that it will not run, even when cold below wide open throttle. It shuts off like a switch below full throttle. The carb runs fine on the mower it came off of, also a 5hp Quantum. I put an inline spark tester on it and it stops firing below full throttle. The kill wire is still off the coil, in fact its removed from the mower completely, plus the blade brake assembly is completely removed as well.
The coil, flywheel, intake, gas tank, and spark plug are all from the other mower. The carb on it now is off a different mower as is the throttle bracket.
I then tried swapping the coil and flywheel off the third 5hp mower but got the same results, it will only make spark at full speed once it gets warm. Those same parts idle just fine on the mower I took them from?

You can do want you want, but that big of a difference in valve clearance is not right. It means that the amount of time fuel is allowed to enter the cylinder and exhaust gases to get out is vastly reduced. This means that less raw fuel will be allowed to enter the cylinder, causing the engine to die. Second, you must be very quick to measure hot clearance, as the engine cools down quickly, which it may be 000 when the engine quits. Just the opinion of an old fart.

EDIT!!!
I’m editing this post as I’m 90% wrong in what I posted. Hot clearances that small will allow the valves to stay open much longer than they should, not closed. The both the intake and exhaust valves will open too soon, plus stay open longer than they should. You may be getting more raw fuel into the cylinder, but you will lose it out the exhaust, due to a longer overlap time. This will result in less power. If you understand what is happening in the cylinder during each stroke, you’ll understand what I’m trying to say. Intake gases actually help to push out exhaust gases during valve overlap. Sorry for giving out bad info.

Has to be something internal like the valves as Rivets said. Try swapping some valves around.

slomo

Valve/tappet clearance will not affect timing or air/fuel passage enough to matter so long as the clearance is not zero. At the very worst, it could cause excessive valve tap.
The Briggs and Stratton shop manual says the clearance should be .005 to .007 for the intake and .007 to .009" for the exhaust valve. A couple thousandths of an inch difference won't amount to enough to make it run or not run.
The only reason I checked it at all was to make sure the clearance hadn't shrunk down to zero which could hold a valve open on the compression stroke. Valve clearances will vary with engine temp as the aluminum block expands as the engine warms up. Since aluminum expands at a different rate than steel, the valve clearances will change with temperature. This is normal.

What's not normal is it losing spark below full throttle. The coil for some reason seems to stop making spark below about 2000 rpm.
At first I thought maybe the 'fixed throttle' engine's carb maybe didn't have a full idle circuit but it runs completely normal and will idle on the other mower with a throttle control. The issue has to be spark to at least some degree, but I can't see how movement of the mower would affect that.
If anything was greatly amiss inside the engine I'd have noise. The cam timing isn't changing or moving, the crank doesn't have excess end play, and the valves are not sticking or held open by 'too tight' valve clearances, and its got good compression.
It makes me think that maybe it won't restart after its hot because the recoil can't get it spinning fast enough to make spark once its hot. But none of that explains why it'll run through a tank of fuel if I just let it sit there on the trailer till it runs out of gas. It never misses a beat. However, if I walk up to it, and push it forward and and back real fast it sputters and gets unstable, it starts acting like its running out of gas and never recovers, it will die even if I leave it sit again. After that point it will restart over and over running a shorter amount of time each time until it will only start and stall. Yet if I left it sit untouched it would have run till the tank was empty.
Like I said before, my first impression was that there was a puddle of water or something on the bottom of the tank, or in the float bowl being sucked up when the momentum forward stopped suddenly. But I've changed the carb, fuel tank, fuel, fuel line and tank several times. I've got a half dozen fuel tanks on the bench here, four carbs, 7 coils, four flywheels, and a box of spark plugs, all of which ran fine on other engines.

If there was something loose enough inside the engine where momentum would make it shut down, I'd hear it, and it likely wouldn't sputter and carry on for a minute before it died.
Someone local said check the float level but the floats in these are fixed, there's no adjustment. They likely don't use enough fuel to require or be affected by a minor difference in fuel level in the fuel bowl.

On the good mower, if I blip the throttle a bit on top of the carb it'll rev the engine higher and return to the fixed RPM.
If I do that on this mower, it will not rev, it dies with any throttle movement It bogs and stalls as the governor tries to return the throttle to the correct speed. On the good mower, I can easily over rev the engine and it returns to the set speed instantly. This mower revs ever so slightly then shuts off as I let go of the throttle.

Keep in mind that this problem came on slowly a couple of years ago when I stopped using it. It started acting up only a bit and got very sensitive to what fuel I used. It wouldn't run on older gas, it got hard to start on month old gas while the other one would burn anything I dumped in the tank. over the course of a few weeks it went from being finicky about gas to stalling every 20 minutes then finally it got to where its at now. That's when I put it away and used a different mower. It didn't happen all at once, as if something broke, it came on slow and got worse till it got to where its at now.
When it happened, I really just thought the carb needed cleaning. Which is what I did first a few weeks ago. That got it running again but since that nothing I've done has changed the situation.

Also, the point when it shuts off the first time isn't really long enough for it to get 'hot', weren't talking three to five passes across a 60ft wide lawn and around a few bushes when it dies the first time. The good mower will run all day tank after tank without any issues.

From your post I guess what I taught for 30 years was all wrong. You keep on making assumptions about the internal workings of the engine, which my experience has taught me will get me in trouble. I would rather inspect, test and verify before stating this or that is fine. That being said I’ll back out of this thread, as I’m not helping you solve the problem.

First off, I've also compared specs measured on the good motor to the one with the issue and both are nearly identical.
If there was any internal engine issues it wouldn't run just fine sitting on the trailer, I let it run through two tanks of fuel now like that.

It rained all week and the grass this week was extra tall, a bit overgrown and a bit wet but I had to get it done today. Not wanting to move the car out of the garage to get at the good mower, I grabbed the one with the problem and mowed with that one. I started in the back yard first, which has about half the grass to cut compared to the front yard. I was able to cut the whole back yard and got one row done in the front yard before it stalled the first time. Again, it was while pushing the mower fore and after vs. pushing it just forward. It still has no kill wire on the coil and the carb, flywheel, coil, and muffler is off the other mower.
When it stalled, I hit the primer bulb about 6 times pretty hard, it fired right back up and sputtered a bit but stayed alive. I did three more rows across the lawn and it started to pop and backfire but it kept cutting. It then started to sputter a bit and out of rage I jerked the thing off the ground and bounced it a few times on the ground with it still running, It sputtered a bit more then smoothed out. It then ran fine for the rest of the yard. I finished the whole yard, shut it down in front of the garage and tried to restart it and it would not restart. A spark tester showed good spark, the plug fired just fine, yet it wouldn't fire on carb cleaner shot down the carb throat. Not even a slight sputter. I let it sit for 7 hours and it started up just fine and has been running on the trailer for the last 30 minutes just fine. What ever is going on its affected by sudden movement or sudden stops.

Carb float levels are adjustable. Using heat, you can bend the plastic tab that pushes on the carb needle.

You need to spend more time testing parts than you do typing.

There is only one spark tester you should be using. Verify your spark.



Air, fuel, spark and compression. You have to prime it to keep the engine running. Tells me a fuel delivery issue. Maybe you need a larger fuel line??

Comparing 2 mowers is a waste of time. Internal parts and their conditions are not the same. The bad running one could have poor sealing valves. You might be checking valve clearance on the WRONG stroke. There is another TDC on most 4 stroke engines. Could have a flat cam or numerous other things.

Lastly you might take some good electrical tape. Wrap the plug wire from the coil to the boot in a healthy layer. Thought was you might have spark leakage when you move the mower. I know you've swapped it all 7 times. Other mower runs with no gas in it.

slomo

I hope you figure it out soon. I got one o a troybuilt pony tiller that will make you pull your hair out. Starts right up, runs fine for a minute or 2 then sounds like it's flooding...but not running rich. Then sometimes it will die and have to run at half choke to run at all.
Carb and tank are clean!
Previous owner even installed a new carb and still acts retarded..

smokediver said:

I hope you figure it out soon. I got one o a troybuilt pony tiller that will make you pull your hair out. Starts right up, runs fine for a minute or 2 then sounds like it's flooding...but not running rich. Then sometimes it will die and have to run at half choke to run at all.
Carb and tank are clean!
Previous owner even installed a new carb and still acts retarded..

Click to expand...

As our resident genius Bertsmobile1 said, there's clean and then there's CLEAN.

A carb can be partially clogged where you can't see it causing your issue.

A new carb means nothing. Most people buy Chinese aftermarket "Gambler Series" carbs trying to save a couple bucks. Then we get to converse with a lot of them trying to get their engine to run proper.

If you have to use any choke at all, after a few seconds, your carb is too lean. Engine is telling you it wants more fuel. Why is it lean? It's dirty with a partial clog internally.

Tillers sit around doing nothing, collecting moisture in the fuel system for how long? Fuel going stale for how long? Is this tiller used daily with fresh fuel added daily? My guess is no. Run the tiller dry before putting it away.

slomo

More than a week later, and the one has somehow fixed itself. It starts, runs, and mows fine since I lost my temper on it and literally beat it on the ground a couple times.
I have three spark testers, one is an inline bulb style, the other is similar to the one in the video above but without the lens, I think its from Snap On, and one called a 'Mag tester', which is basically a spark plug with an alligator clip on one end with two protruding electrodes.
When I say it has no spark, it has NO spark, I can hold the coil wire and spin the motor with the electric starter.

At this point, I have two fixed, one 6.5hp took a carb cleaning, new fuel hose, cleaning the tank, a new coil, and a used flywheel to get it going, it runs okay but its a tired mower otherwise with a 'too short' handle for a big guy.
The second one has a new coil, freshly cleaned carb and tank, and a new fuel hose.
All have new fuel lines, (1/4"), new spark plugs, new blades, and all have had their carbs cleaned, (or replaced). Plus I have a box of new coils, some Briggs and Stratton, a few are Stens.
Those that won't run, have no spark, and have the kill wire removed from the coil.
The Stens coils have gotten spark back in a few while the new BS coils didn't, yet they fire on other motors?
A few of the coils that won't fire on one motor will fire fine on another, but won't run. They fire erratic regardless of the gap or ground.
On those that run and die, they're loosing spark when they die, I can hold the plug wire in my hand, there's no spark. Some run a bit longer, some only a few seconds.

Even if there were a valve issue, its not likely on every one of these, and if there were that big of an issue with the valves or something internal, it wouldn't 'fix' itself in a matter of minutes just sitting there, or come and go at will. It also would not act like an engine running out of fuel when it died.
The one I've been dealing with lately is another 5hp, it has spark cold but loses it after it gets warm. Its got a new flywheel, coil, carb, tank, spark plug, fuel hose, and blade. I pump the primer three times, it starts right up and runs fine. If I let it sit there, it'll run for hours till the tank is empty. If I go to use it, it dies before I make it to the front lawn, just rolling it across the driveway.
It will restart fine, mow a row or two and start to sputter and die. It'll do that three or four times before it refuses to run at all. At that point, it has no spark.
I've swapped the coil and plug 5 times, swapped the flywheel twice, no change. That's by far my best mower in that I like how it mulches the grass.
Yes, I've tried shooting fuel in the carb, it makes no difference, there's no spark. Yes, it has strong compression when it dies. It acts like its running out of gas.
It seems to happen the first time I push the mower forward and pull it backwards, as in mowing under a bush or around obstacles.
It acts as if something is floating in the fuel system and sudden movement causes it to get a taste of water or bad gas, but the tank and cap are new, the carb is new, and the fuel is fresh. There's nothing in the fuel system, I've been over it a dozen times now.
I'm getting close to just yanking the Quantum motor off and sticking an old 3.5hp on that one. None of those have ever given me so much as an ounce of trouble.

From what you have just posted then you either have the wrong coils, defective coils or the wrong flywheel or defective flywheel or have been installing the coils upside down.
Or a combination of any or all of the above.
Downside of using similar castings and flywheels with the same tapper on them is you can fit all sorts of wrong parts.
If it was a twin motor then I would be thinking RF interfearance with the timing chip

bertsmobile1 said:

From what you have just posted then you either have the wrong coils, defective coils or the wrong flywheel or defective flywheel or have been installing the coils upside down.
Or a combination of any or all of the above.
Downside of using similar castings and flywheels with the same tapper on them is you can fit all sorts of wrong parts.
If it was a twin motor then I would be thinking RF interfearance with the timing chip

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And possible non resistor spark plugs? My guess is those would interfere with the timing.

slomo

yardiron said:

More than a week later, and the one has somehow fixed itself. It starts, runs, and mows fine since I lost my temper on it and literally beat it on the ground a couple times.
I have three spark testers, one is an inline bulb style, the other is similar to the one in the video above but without the lens, I think its from Snap On, and one called a 'Mag tester', which is basically a spark plug with an alligator clip on one end with two protruding electrodes.
When I say it has no spark, it has NO spark, I can hold the coil wire and spin the motor with the electric starter.

At this point, I have two fixed, one 6.5hp took a carb cleaning, new fuel hose, cleaning the tank, a new coil, and a used flywheel to get it going, it runs okay but its a tired mower otherwise with a 'too short' handle for a big guy.
The second one has a new coil, freshly cleaned carb and tank, and a new fuel hose.
All have new fuel lines, (1/4"), new spark plugs, new blades, and all have had their carbs cleaned, (or replaced). Plus I have a box of new coils, some Briggs and Stratton, a few are Stens.
Those that won't run, have no spark, and have the kill wire removed from the coil.
The Stens coils have gotten spark back in a few while the new BS coils didn't, yet they fire on other motors?
A few of the coils that won't fire on one motor will fire fine on another, but won't run. They fire erratic regardless of the gap or ground.
On those that run and die, they're loosing spark when they die, I can hold the plug wire in my hand, there's no spark. Some run a bit longer, some only a few seconds.

Even if there were a valve issue, its not likely on every one of these, and if there were that big of an issue with the valves or something internal, it wouldn't 'fix' itself in a matter of minutes just sitting there, or come and go at will. It also would not act like an engine running out of fuel when it died.
The one I've been dealing with lately is another 5hp, it has spark cold but loses it after it gets warm. Its got a new flywheel, coil, carb, tank, spark plug, fuel hose, and blade. I pump the primer three times, it starts right up and runs fine. If I let it sit there, it'll run for hours till the tank is empty. If I go to use it, it dies before I make it to the front lawn, just rolling it across the driveway.
It will restart fine, mow a row or two and start to sputter and die. It'll do that three or four times before it refuses to run at all. At that point, it has no spark.
I've swapped the coil and plug 5 times, swapped the flywheel twice, no change. That's by far my best mower in that I like how it mulches the grass.
Yes, I've tried shooting fuel in the carb, it makes no difference, there's no spark. Yes, it has strong compression when it dies. It acts like its running out of gas.
It seems to happen the first time I push the mower forward and pull it backwards, as in mowing under a bush or around obstacles.
It acts as if something is floating in the fuel system and sudden movement causes it to get a taste of water or bad gas, but the tank and cap are new, the carb is new, and the fuel is fresh. There's nothing in the fuel system, I've been over it a dozen times now.
I'm getting close to just yanking the Quantum motor off and sticking an old 3.5hp on that one. None of those have ever given me so much as an ounce of trouble.

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Make sure the two coil mounting tabs are sanded clean with fine paper. And the coil is free of dirt and oil. Lastly the mounting areas are clean to bare metal so it can ground itself and make spark.

slomo

smokediver said:

I hope you figure it out soon. I got one o a troybuilt pony tiller that will make you pull your hair out. Starts right up, runs fine for a minute or 2 then sounds like it's flooding...but not running rich. Then sometimes it will die and have to run at half choke to run at all.
Carb and tank are clean!
Previous owner even installed a new carb and still acts retarded..

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Check for vacuum leaks. Parts heat up and expand. Spray some carb juice around the carb mounts.

slomo

Over heating can cause the engine to die in 20 minutes. Clean the engine block, under flywheel and all fins. This is a yearly item in your engine manual. Neglect this and you are looking at engine damage.

slomo