Help!!!!!!!!
I have a old snowblower that I aquired last year 1970b/s motor
I switched it to electronic ign. and rebuilt carb. It started on the first pull
ran great after about 15 minutes of running on high it would start to
stumble if i adjust mixture screw it would smooth out for 3-5 min.
I took the carb apart again had it dipped to try and clean it better
same problem. I purchased a new carb. and still had same problem.
This summer I took the valves out to inspect the valve seat and
guides. Exhaust valve guide is a little worn but not terrible.
I lapped the valves in and removed all the carbon build up, changed the oil
and thought I was good to go. Same problem only seemed worse
and oil was coming out breather. I drained some oil and it was back to it's old
self. I'm thinking it's getting oil in the combustion chamber and it is changing
the mixture. note it will idle forever. Anybody seen this before???

its possible the coil may be failing under the heat, it will run hotter when running full rpm's that is if it stops running, and won't restart unless it cools some?. if your getting oil into the combustion chamber, won't do much but use oil, smoke and carbon everything up quick. spark plug would probablly look oily as well. as for adjustments, 1.5 times out from snug, then fine tune when warm.

Thanks Bugman
I Dont Think It A Coil Because If Put It To Idle It Will Keep Running
I Leaning Towards Something Mechanical Like The Valves

Tony, I think you may have a possibility of a few things going on here. What I would check for first is make sure the valve clearance is correct on both intake /exhaust.Check rpms , too high will cause this , excessive oil in the base and a faulty oil seal on the dip stick will cause this.Check the plug hole on the crankcase breather, make sure that the oil can drain back into the crankcase. Your getting presssure in the base for some reason, maybe the valves are not completely closing or bad rings causing blowby.this causes you to lose your crankcase vacuum with is very important for the engine to operate properly.If you have access to a leak down tester , this would pin point the problem more effectively .I hope this helps you to correct your problem, good luck & happy fixing

Snow Ball Thanks For The Suggestions I Will Check The Valve Clearance

Thanks For All The Advice I Broke Down Today And Bought A New Engine From Small Engine Wharehouse For $275.00
I May Try And Tackle This Old Motor In The Spring More As Pride Thing Again Thanks For All The Input