70 hp johnson top cylinder trouble

[ddswulf]

i have a 1977 70 hp that is having problems under load. i have determined that top cylinder is problem, but can't figure out what. with engine running and plug out but in wire, it fires normal. with engine running and plug in i pull wire and it only seems to fire intermittently. could this be the coil, if so how do i know for sure. any help would be appreciated.

 

[ob]

Re: 70 hp johnson top cylinder trouble

Try swapping coils and see if you're symptom moves.Inspect the coil cases closely for any cracking or fractures as that is a sure sign of them being on their way out.