I'm trying to get the Cub running again. It quit a while back, and ever since it will only backfire(frontfire?) through the carb. A new set of points didn't help.
Any help will be greatly appreciated. The push mower is a drag.
If it's popping through the carb,the intake valve is probably hanging up or at least working slow.I've already been able to free them up by shooting WD40 into the carb but it depends on what's causing it to stick.
Aparently it has been backfireing alot so I'm with Kabitze on this one it's fly wheel key. kiss , after you get the new key in - check the carb and see if it's running lean and the plug wire under the sheet metal is not chafed and for good measure change the spark plug .
If you set your points with a timing light or if you have a magneto ignition, then it could be the flywheel key. Otherwise that’s probably not it (the points on a K-301 get their spark from the coil not the flywheel).
If it were mine, I think I would probably pull the cylinder head and see what’s going on in there, if the head hasn’t been pulled in awhile you will probably want to de-carbon it anyway. Turn the motor and make sure the valves are operating properly.
She was running at full speed under load when she quit. Cranks really hard now too. I think the flywheel is on the driveshaft end so the motor will have to go back on the bench. Makes perfect since, it's acting like a motor with a jumped timing chain. Never gave the key a thought.
Like CCH said, They're not timed off the flywheel. I would also pull the head first (much easier) carbon or a broken cam or gear. check your valve timing. Could also be a broken valve spring. Good luck and keep us posted.
I think you have an intake valve problem. Pull the head or get a compression reading. I have never seen myself a broken flywheel key. Hard cranking could be a broken acr spring. Worst case is a broken cam stuck on intake stroke. This I have seen. But a compession test will tell all.