Motorcycle engine?
Answers:
youn probably have a valve stuck open but don't worry it will free up just by running it unless it is bent./
normally the carb,s will need cleaning,as in time petrol goes back to a solid state you will find blocked jet,s ,get some good quality spray cleaner and take your time as you only want to take them off once.
No vacuum? That doesn't sound good. Have you tried a compression test? Also as others have suggested, make sure your carbs are clean.
Stuck valves.
Most of the other answers cover most options the only other thing it could be is that the piston rings might be stuck in their grooves and not springing out to the side of the cylinder thus loss of compression ( suck ) give that a look.Good luck
Worn valve seat?
the cylinder wont fir if there is no compression, as its unable to compress the gas .
Do a compression check. make note of the reading, pour a small amount of engine oil in the cylinder and try the test again. if still low, check your valve clearances.
Perhaps one of the valves is stuck?
if you have no vacuum you have no compresson. possibly scratched piston or bad ring.
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