Troubleshooting a Tecumseh ohv130

[38racing]

We had a mtd with this engine left at our church scrap metal drop. My friend quickly sold it so i just did a quick once over. Added the usual shutoff valve along with new fuel filter , fresh oil and air cleaner. It started fine and I did a short test cut. I delivered it to the buyer. I got second hand feedback that it had an issue. Then that it was ok again. Latest ws it again had issue and buyer thinks it's the flywheel key. I finally picked it up. Buyer was about to attempt checking flywheel key. He admitted to having an incident in the ditch that he felt could have sheared the key. I brought it home. What I've found and done. Noticed that slightly overfull with oil but not gassy. Iirc the first report of a problem had him saying it was low on oil. Not likely but he may have added some. I removed plug and cranked it. No sign oil of fluid in cylinder. I replaced plug. It started fine but slowed and then recovered. I did sense a slight miss at full rpm. I then checked coil gap which appeared to be .006 to .008. I reset coil to .012. I noted that plug is a ngk br9es. Spec is champion rn4c which crosses to br6es so I replaced for now with a used br6es from my plug bin. So now situation is that it starts fine at full rpm but if I reduce throttle to lower rpm and then quickly increase throttle it stumbles and might even stop. It will go up if I slowly increase the throttle. When it stumbles to a stop it may even backfire. My thought is that it's not flywheel key as it will start and run pretty much normal. I am going to check valve clearance but I'm leaning towards the carb and fuel supply. Flow to carb seems to be sufficient and the small remaining fuel in tank had no sign of water and now I added fresh fuel. The backfire is similar to times I've had engine backfire as it ran out of fuel. The carb is the Tecumseh plastic bowl model with everything in the bowl. It has the o rings that can be a problem. Any thoughts?

[KE4AVB]

I wish I could be of help but Tecumseh engine were before my time as a small repairman. I depend on help from folks like you on my problems especially since we lost T-man. He just vanished.

Now I rarely even see a walk behind with a Tecumseh engine.

One thing I would do would be to check the valve clearances.

[bgsengine]

It's gonna be a carburetion problem. Never fails with a Tecumseh - I have had several engines in various sizes from Tecumseh post-EPA rules, and they all were just the carburetor being just a teeny bit too lean. Since the carburetors were not adjustable, it leaves you with very few options - but your stumble from idle to full throttle means it'll be the idle circuitry - However, may be worth checking valve clearances and maybe even a leakdown test to check for any valve trouble. But all else fails, I might suggest finding an adjustable aftermarket carburetor to fit and see if you can solve it by dialing in the adjustment.. When they were new they probably ran perfectly fine in that exact setup, but as they break in and age a little, obviously they'll lose a tiny bit of compression, they'll get slight play in valves, and so on. - None of the individual bits by themselves being enough to cause any problems, but when put all together and added up, results in the fuel mixture being delivered by those fixed carburetor jets being just slightly insufficient.

So I would be 99.9% sure in saying your issue is gonna be with the carburetor & fuel delivery, but whether it is actually fixable, (or worth fixing) is something else, unless you can find an adjustable carburetor that will do the job.

[38racing]

Thanks. I doubt this carb has an adjustable replacement. It's pretty straight forward. The complete bottom used to be a reasonable price but might not be with current trends. First time I serviced one of these the nozzle flew by my head when the spring let go. Found nozzle right away and spring weeks later.

[38racing]

I checked valves. Spec is .004 and both were .005 so I left them alone. Leakdown at 30 psi was 13. Carb appeared clean in that no crud anywhere. O rings were actually in good shape but I replaced the one on the nozzle. Made sure main jet was clear. Carb is actually quite straight forward for checking passages. There is an idle jet in the tower of the plastic bowl. Fuel comes up from the bowl from same spot that feeds main jet. It didn't seem to pass carb cleaner very well. Sort of tricky holding finger over nozzle feed tower. Rather than use the usc I just persisted with carb cleaner and air. Finally got good flow. I replaced needle and seat and the gasket between bowl and body. Put new br6es plug in it. Runs fine now . did a 15 minute cutting and returned it to our buyer.