by bgsengine » Tue Jul 06, 2021 8:05 am
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.
How poor are they who have not patience. What wound did ever heal, but by degrees? - Iago (Othello Act II, Scene 3)