Johnson 35 HP starts missing when warm

[CHM]

Maybe one of you has heard of this. My 1978 Johnson runs great...until it warms up. Example - I can go wide open to a spot, fish with the bow mount for a while, and then take off for a new spot and it starts missing. It doesn't seem to be just running on one cylinder, it's like a miss or the timing is off. I have rebuilt the carb and put in new plugs, as well as a different fuel tank with new gas and oil.

Tonight I test ran it and it went for 10 minutes at half throttle to wide open before it started missing. I put the hose on it in the driveway and warmed it up , then put a heat gun to the electronic ignition and the coils to see if they were failing when hot. I couldn't really tell if that mattered or not.

Any ideas?

[jgeatz]

Just a thought, have you checked the primer bulb when it quit? Sounds like a fuel problem to me. Those bulbs do go bad and that will starve her of gas.

[CHM]

Replaced it - no help.

Thanks

[iffy]

It sounds to me like you may have a bad head gasket. When they first start to go (between cylinders) they sometimes seep when they get warmed up. Pull the plugs when it acts up and see if they look washed. That will be the indicator. If so, its an easy fix. About 40 bucks for a head gasket, and a couple more for the water jacket gasket, and an hour or so, and you'll be good to go.