Carb repair

[chuckpen]

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

Broken or weak governor spring?

 

[Freddie21]

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

 

[Freddie21]

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.

 

[bertsmobile1]

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 .

 

[Freddie21]

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!

 

[VRR.DYNDNS>BIZ]

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?

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!.

 

[barny57]

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,

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

 

[elmrfudd]

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.

 

[Freddie21]

good advice, will check

 

[elmrfudd]

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.