Muffler sounds funny, I would start looking there for blockage...after you have checked your flywheel key as others have mentioned.
If your spark plugs aren't new, I can't imagine installing new heads without new sparks, but hey, I can't blame a guy for saving $10 whenever possible.
Holding a spark plug against the ground is 'good', but it really doesn't tell you much as compared to a spark plug working under pressure, that is why professionals use 'spark testers' and other equipment. Occasionally even a new spark plug turns out to be a dud.
wwxx
If your spark plugs aren't new, I can't imagine installing new heads without new sparks, but hey, I can't blame a guy for saving $10 whenever possible.
Holding a spark plug against the ground is 'good', but it really doesn't tell you much as compared to a spark plug working under pressure, that is why professionals use 'spark testers' and other equipment. Occasionally even a new spark plug turns out to be a dud.
wwxx
