Not at all uncommon for a valve to stick open on an engine that has
been poorly stored or stored a long time - or even on an older engine
with carbon buildup on the valves/stems - regardless how it is stored.
One "too" that helps free up stuck valves is a product called
"avblend" that attacks carbon and lead buildup on the valve
stem/guide. It is used by many AMEs on aircraft engines with "morning
sickness' (running rough when first started cold due to a slow/sticky
valve) Available from places like Aircraft Spruce.
Works a bit better and faster than MMO (Marvel Mystery Oil) but costs
a lot more too.
Most likely cause is a valve stuck open from sitting. If it is a
flathead pop the head off and squirt penetrant around the guide of the
stuck open valve and tap the valve gently down (piston at BDC)
If OHV remove muffler and carb - soak valve stems with penetant remove
rocker cover and gently tap on the valve stem to free it up so the
spring can pull it closed. If you can't get it closed that way the
head will have to come off and the valves worked from there.
Then when you get the valveclosing and the engine running, run a bit
of top lube, like MMO in the gas. Some mmo in the oil won't hurt
either. Get it warmed up and change the oil.
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