Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Check the throttle linkage and look at the carburetor throttle plate, is the linkage opening the throttle flap fully when engine is OFF. Lack of rpm is typically just the throttle not opening fully.
If compression was problem, it would not start. It starts, so that is ok. You have new carburetor, is it adjustable? Have you turned the high speed screw while throttling it?
If you dribble fuel into the carburetor while running at high speed does it increase in rpm?
Did you try running without the muffler/spark arrester?
When did it last run correctly? Are you using premixed fuel?
Coil is not loose, throwing off the spark/timing?
I doubt it. That would only leave the timing key on the flywheel.
would think it would make it hard to start, but all other items seem to have been checked..
I'm with you, makes no sense!
Crankshaft seals can let air into the crankcase , but is usually shows as hard start.
It may be crankseals . But i personally have never seen crankseals do this.
Iwill opt out and see if anyone else can add anything. sorry.