Marine: Boating, Sailing, PWC, GPS and Navigation - crazy motor

i have a 72 or 76 johnson that will run with a pop every few seconds but if you take the top spark plug wire off then it runs like a a brand new motor. put the wire back on it starts poping and bogging down.i have changed the spark plugs. what in the world do i need besides a new boat motor?

Welcome to the forums.

Can you post the exact year and model number? The symptom you describe sounds like a shorting or worn-out spark plug wire.

How old are the spark plug and coil wires?

I have seen this on 2 stroke ATV engines and it was a bad coil but usually under load. Unfortunately this may be one of those problems where you have to throw non-returnable parts at it to see if it fixed it. Are the coils the same and can you swap it to another cylinder and see if the problem follows it?

This is a shot in the dark, but is it possible that you have a hole in that one piston? I cringe as I ask that but we all know that it happens.

probably just to coil or the points. they`re under the fly wheel.
and you`ll need a fly wheel puller to get to them.

i made one one out of a flat peice of steel with 3 holes and 1 in the center with a bolt & nut to push into the crankshaft.

i would try the coil first as it is easiest.
is the plug fouled at all? maybe a little water is seeping into the cylinder through a bad gasket.

can you post a little more about the motor?

hp?

# of cylinders?
# of coils?
pull start? electric start?