You have an engine
cylinder that is not as strong as the rest, and you have
determined that it is getting spark, but something is wrong
A simple tool that can
sometime locate the fault is the following:
Take an old spark plug
that fits the engine, remove all of the porcelain and the
center electrode, leaving just the outer shell. Braze an air
fitting into the shell.
Now turn the engine over
until the piston in the suspect cylinder at TDC (top dead
center) on the compression stroke. Insert the modified plug
and apply 60-80 psi air to the cylinder. You want enough air
to follow through the procedure, but not enough to turn the
engine. With air pressure in the cylinder, listen 1. if you
hear air bubbles, it may be a leaking head gasket; 2. if you
hear air in the exhaust, it may be a leaking intake valve; 3.
air coming up through the carb, it may be a leaking intake
valve; 4. a hissing from the oil fill tube or dipstick tube
would indicate a piston or piston ring problem.
This simple homemade
device can save a lot of time in diagnosing a problem.