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I have questions regarding the cleaning of carbs. I disassemble them then soak in a water\Purple Power solution using a ultrasonic cleaner. Then I blow it out with air, spray with cleaner, use small wires in passages, clean with cleaner and finally shoot with air. This works with carbs that have removable jets. I have issues with the one with Welch plugs or none adjustable jets. I have not removed any plugs as I don't have replacements. In the case of the air\fuel mixture adjustment having holes under the Welch plug, if I remove it and clean the holes, does that new plug have to make an air tight seal? How about the plug inside the carb? I haven't seen a Welch plug assortment kit for small carbs, just for a certain car engine model. If anyone knows of one, please let me know.

Thanks all,

Freddie21 said:

I have questions regarding the cleaning of carbs. I disassemble them then soak in a water\Purple Power solution using a ultrasonic cleaner. Then I blow it out with air, spray with cleaner, use small wires in passages, clean with cleaner and finally shoot with air. This works with carbs that have removable jets. I have issues with the one with Welch plugs or none adjustable jets. I have not removed any plugs as I don't have replacements. In the case of the air\fuel mixture adjustment having holes under the Welch plug, if I remove it and clean the holes, does that new plug have to make an air tight seal? How about the plug inside the carb? I haven't seen a Welch plug assortment kit for small carbs, just for a certain car engine model. If anyone knows of one, please let me know.

Thanks all,

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Yes it must be an air tight seal, that why replacement welch plugs are domed. In the case of the SV590 Nikki the welch in the repair kit. And most carburetors repair include the welch plugs. Even SV590 has over six pages of different spec numbers so for the correct you must have the spec number too.

And you won't find a welch plug assortment kit for small engines and even if there is one, 95+% chance that the plug you need wouldn't be in it.

Personally I have never removed a welch plug since I started using an USC. Now I do have a few to fall out that has to be replaced.

Even after cleaning with the USC, the carb surges. I was thinking it was due to not cleaning the jets under the plugs. Do you have this issue?

Surging when ?
at idle ?
when driving ?
with blades on ?
While the bulk of surging is from insufficient fuel, it can also be an air leak on the engine side of he main jet so a gasket or manifold leak .

Surges at any speed in Neutral and no load. New gasket on engine side, no air cleaner mounted (no effect when mounted) and sprayed around carb with cleaner to check for leaks. Has happened many of times with rebuilt (cleaned) or new Amazon carbs on different engines. Always set valve clearance first and verify good fuel and flow to carb. I have not adjusted governor.

Freddie21 said:

Surges at any speed in Neutral and no load. New gasket on engine side, no air cleaner mounted (no effect when mounted) and sprayed around carb with cleaner to check for leaks. Has happened many of times with rebuilt (cleaned) or new Amazon carbs on different engines. Always set valve clearance first and verify good fuel and flow to carb. I have not adjusted governor.

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Sometimes shortening the carburetor linkage spring, that attaches to the Governor helps improve hunting and surging. Make sure intake has no cracks or leaks, good gaskets (so no air leaks. Sometimes very slightly enlarging the pilot (idle) jet helps eliminate hunting and surging.

Freddie21 said:

Surges at any speed in Neutral and no load. New gasket on engine side, no air cleaner mounted (no effect when mounted) and sprayed around carb with cleaner to check for leaks. Has happened many of times with rebuilt (cleaned) or new Amazon carbs on different engines. Always set valve clearance first and verify good fuel and flow to carb. I have not adjusted governor.

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As said governors can cause this but there are other possibles. Usually if it smooths out when you hold the throttle at the carburetor is it the governor but if not then it is in carburetor. This why you first determine where the problem exists and go from there. I lean burn and rich burn issues with carburetors. Usually rich burners either something you missed or someone in the past resized a jet. Also with the clones anything is possible.

I have had Kohler Courage singles to surge after determining that governor was the issue as it was play in the governor itself and I had to trick set the linkage to fix them. Other times it is the carburetor on an engine using governed idle where the bare minimum idle is not set correctly. Briggs V-twins usually have a governed idle setup.

So it is not as simple at times as this or that is the problem but a combination of problems. Only lots of experience will help fine your skills.

Tiger Small Engine said:

Sometimes shortening the carburetor linkage spring, that attaches to the Governor helps improve hunting and surging. Make sure intake has no cracks or leaks, good gaskets (so no air leaks. Sometimes very slightly enlarging the pilot (idle) jet helps eliminate hunting and surging.

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And sometimes if someone had done this in the past it can actually cause the problem. Just depends on what the spring purpose is. On Honda engines there is a delicate balance even on the slack prevention springs. I once had a pressure washer with a Honda engine that surging like crazy where someone did this. New spring resolved the issue.

Appears only the carb was removed. The surging goes away if I either choke it 80% or hold the throttle arm preventing the governor from pulsing it. I will do a static adjustment this weekend. Thanks

did you remove and clean the main jet, idle jet and emulsion tube from carb?

I do not know about this carb but have been told there can be a "final screen" in some carbs on the fuel inlet, between the inlet and needle seat. Some carb clean in reverse as it were.

I'd also check your float is actually working and allows fuel to the correct height in the bowl. Could be sticky needle/seat or not "floating" high enough.

Don't think it's a carb problem as both carbs are identical and out of working machines. If I hold the throttle arm it runs great at any speed. Carbs have been completely cleaned. Thanks man

Freddie21 said:

Don't think it's a carb problem as both carbs are identical and out of working machines. If I hold the throttle arm it runs great at any speed. Carbs have been completely cleaned. Thanks man

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Broken or weak governor spring?

All springs in good shape. It was suggested I adjust the governor. I'll do that soon.

Thanks to all that provided suggestions. I got it licked by backing the idle mixture screw out 2.5 turns. This engine runs great now. But, I run into this constantly and will keep these all in mind. Especially, the governor adjustment. Wouldn't think a carb replacement would require it, but I will try.

governors CLOSE the throttle so when they are working they SLOW down the engine
When a governor fails the engine races away uncontrolled .
Mower engines run on the idle jet alone till there is a big load on the engine such as driving up a big hill or running the blades.
When the governor allows the engine throttle plate to open fully then & only then does the main jet supply the fuel to the engine .
This is why engine makers use terms like "High Idle " which is in fact running speed for most engines ( 2700 to 3600 rpm )
Engine makers also use the term "Low Idle " which is the slowest the engine should be run with the throttle lever ( the one you move ) set to it's lowest position which is 1200 to 1700 rpm .
It is unfortunate that no one bothered to invent new names for the jets used in governed mower engines but just used the same names used in manually controlled engines found in cars & motorcycles.
So your problem all along is the "No Load" jet was closed down too far .
The other thing that many fail to understand is the jets do not turn on & off like a light switch unless there is a check valve ( as found in some cube carbs ) so at WFO the "no load" jets are still supplying up to 10% of the fuel to the engine so a stopped down "no load" jet as was in your case will drastically effect the running of the engine at all speeds as you have just found out .

It is one of the big drawbacks of WWW forums that those trying to provide the help have nothing to work on but the words posted by the thread starter.
If we were standing there next to you watching the mower & what you were doing then we would have ( hopefully ) picked up on the stopped down "no load" jet a long time earlier as most of us could visually see that the "no load" needle was protruding too far into the carb throat.

People also fall into the trap of thinking that all new parts are pug & play which they are not and if that particular carb is used on a lot of engines it will be "factory set " to the smallest engine it was fitted to . if in fact it was adjusted at the factory at all .

Glad you nutted it out & sorry we did not pick up on it earlier .

Your expanation is greatly appriciated. Videos, most times, don't explain in enough detail. This carb was nice as it had the adjustment. Replacements for the Nikki come pre-jetted and not adjustable. Where is the same 'no-load' jet on them so as I can increase the diameter, if necessary. This is the most common engine I see. If you would like a picture of a replacement carb, please let me know. Great info!

Freddie21 said:

Even after cleaning with the USC, the carb surges. I was thinking it was due to not cleaning the jets under the plugs. Do you have this issue?

Click to expand...

Once a welch plug is removed and reinstalled with a new one, seal the outside with nail polish. Nail polish will not dissolve under petroleum products. I use guitar strings as fine wire cleaners. To determine the root cause of a hunting operation, hold the throttle at various moderate settings and find the point at which the problem exists. If it runs good no matter what normal rpm, it is governor hunting. If it nearly stalls or worse at low speed, it is the low speed circuit, etc. If you find it is the carb and cannot get the (if needed) welch plug, order a carb!.

Freddie21 said:

I have questions regarding the cleaning of carbs. I disassemble them then soak in a water\Purple Power solution using a ultrasonic cleaner. Then I blow it out with air, spray with cleaner, use small wires in passages, clean with cleaner and finally shoot with air. This works with carbs that have removable jets. I have issues with the one with Welch plugs or none adjustable jets. I have not removed any plugs as I don't have replacements. In the case of the air\fuel mixture adjustment having holes under the Welch plug, if I remove it and clean the holes, does that new plug have to make an air tight seal? How about the plug inside the carb? I haven't seen a Welch plug assortment kit for small carbs, just for a certain car engine model. If anyone knows of one, please let me know.

Thanks all,

Click to expand...

I wouldn’t mess around with the Welch plugs , I have a few all snowmobile’s with them carbs very hard to fine parts I would say clean it the best you can and go from there

Another check for surging is to check for side play in your throttle shaft. Wear in that shaft or guides will cause your engine to suck additional air around the shaft, leaning it out.

good advice, will check

If you have slop in your throttle shaft, the surging will likely stop when given a shot of starting fluid at the top of the shaft while running.

Just a related piece of advise... these small carb jets seem to take nothing to clog them, causing all sorts of problems. A few years ago I finally decided that as soon as I got a small motor device I would put a fuel filter (get the lowest micron size available) in line with the gas hose from the tank to the carb. Its a small investment for worry free operation. You can buy a whole package of them on eBay for not much $$. And, during spring startup I put some Sea Foam in with the fuel to get rid of any fuel residue that may have developed during the winter storage. This is my routine... you might consider something like this for the future. I have several garage sale finds.. edger and shredder and I am seldom lucky enough to find anything that doesn't require carb work... I also have an ultrasonic cleaner. I use 80% rubbing alcohol as a cleaner for carbs. Probably not the best cleaner but it does get them clean. A UT cleaner is nice but its not the ultimate solution. You still have to take some wire (get a pack of welding torch, tip cleaners, below...) to clean out those pesky little passages in the carb. The smallest ones work well and they have a bit of an abrasive finish which will work out anything hard. Can't beat 'em...

schleeb said:

You still have to take some wire (get a pack of welding torch, tip cleaners) to clean out those pesky little passages in the carb. The smallest ones work well and they have a bit of an abrasive finish which will work out anything hard. Can't beat 'em...

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Actually be the worst thing you can use on some carburetors especially the small cube carburetors use on handheld equipment. several of the passage actually have rubber check valves which are destroy when wire probed.

StarTech said:

Actually be the worst thing you can use on some carburetors especially the small cube carburetors use on handheld equipment. several of the passage actually have rubber check valves which are destroy when wire probed.

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Yup, folks bring in stuff they tried to clean the carb on And used carb cleaner and a bread tie wire and ruined the carb. I can fix pretty much anything on a cube carb but the check valve. Got a box of them with bad check valves. Really shouldn't use carb cleaner or brake kleen on cube carbs or pokey wires.

Fortunately, I have never encountered those passages with the rubber check valves on a four cycle engine, but I use the torch cleaning wires all the time, and they are great as long as you don’t ream out the hole with a wire with too large a diameter. When I use the ultrasonic cleaner, I use about an 8:1 mixture of water to Simple Green liquid cleaner, and a tablespoon of Dawn dish soap. I strip the carb down totally, including all jets inside the main jet port. Usually I cook the carb at about 180 degrees for an hour+, depending on how gunked up it is. I put all the small parts in the bowl while cleaning. I also pull out the small plastic jet (on many carbs) and wire clean that. That plastic jet has two small seals and a tiny port that must be clear or your engine will surge. I don’t sonic clean the plastic jet at high temps, as it will swell and be very difficult to re-insert. After cleaning, I blow out all residual water with compressed air, then reassemble. If you’re not going to replace the brass seat, I would clean it out with a dab of toothpaste on a Q-Tip until swabs come out clean. Failure to do this may cause needle/seat failure. Just a tip to let everyone know what has been very successful for me in the past. God bless you all!

Lots of good tip and I apricate them all. I do most of them now and haven't run across the cub carbs as I stay away from 2 strokers. I was wondering what a good cleaning solution is and I'm close using Purple Power.

Thanks for the tips... but I don't believe I've encountered any rubber gaskets/seats yet. I'm mostly Briggs and Stratton motors and the like. I would like to get a better cleaning solution though and save my alcohol for some other purpose. Even though I have close to 15 gals. of it. (Home Depot had 80% ethyl alcohol in gallon jugs of the stuff, on clearance, for 75 cents a gallon! Couldn't pass on it...bought all that was left, 14 gallons) One thing I'm going to check out is the NRA's cleaning solution formula that they recommend for cleaning cartridge brass. Published a long time ago and it works very well in my UT cleaner for my rifle brass. Their formula is:

1 Pint water (I use distilled water)
1 cup white vinegar (5%)
1 tablespoon salt
1 teaspoon dish detergent (I use Dawn)

It cleans the hell out of cartridge brass... but it dulls the finish a little, so I run it through my vibratory brass cleaner with a mix of walnut shells and stainless steel pins and common BBs, for a BB gun, to polish them back up. I'll post next time I clean a carb.

schleeb said:

Thanks for the tips... but I don't believe I've encountered any rubber gaskets/seats yet. I'm mostly Briggs and Stratton motors and the like. I would like to get a better cleaning solution though and save my alcohol for some other purpose. Even though I have close to 15 gals. of it. (Home Depot had 80% ethyl alcohol in gallon jugs of the stuff, on clearance, for 75 cents a gallon! Couldn't pass on it...bought all that was left, 14 gallons) One thing I'm going to check out is the NRA's cleaning solution formula that they recommend for cleaning cartridge brass. Published a long time ago and it works very well in my UT cleaner for my rifle brass. Their formula is:

1 Pint water (I use distilled water)
1 cup white vinegar (5%)
1 tablespoon salt
1 teaspoon dish detergent (I use Dawn)

It cleans the hell out of cartridge brass... but it dulls the finish a little, so I run it through my vibratory brass cleaner with a mix of walnut shells and stainless steel pins and common BBs, for a BB gun, to polish them back up. I'll post next time I clean a carb.

Click to expand...

That formula is very close to my weed killer formula

My dad used to reload center fire cartridges when he was alive, and he tumbled his brass with water, Palmolive dish soap and Lemi-Shine dishwasher additive, using stainless steel pins as his medium, and his brass came out clean and shiny, but always used purified water with no contaminants. I’ve cleaned some coins and jewelry with that protocol, and it did a great job! I’ve not tried it on carburetors yet, although I’ve considered adding a squirt of Lemi-Shine in my USC.