71 johnson 2 horse overheating

[twocyclemania]

Picked up a 71 Johnson 2 horse that was obviously used very little and has no signs of salt corrosion. I installed a new impeller and the rubber grommet at the top of the pump where the copper pipe attaches. The pump looked good. Anyway, the motor is overheating. The impeller key is in place. It does put out exhaust and mist from the leg holes. The intakes are clean. I took it apart and flushed water up the copper pipe and there does not appear to be any restriction. The only thing I can think of that could be a problem is where the pipe meets with the head. I imagine there is a grommet at the top. Is this a likely candidate? Is there anything that's a common problem with these motors? Anybody familiar with these engines and what the problem could be?

 

[nwcove]

Re: 71 johnson 2 horse overheating

not framiliar with that motor, but do a compression test. could be a head gasket issue.

 

[twocyclemania]

Re: 71 johnson 2 horse overheating

Removed the powerhead today. The rubber grommet at the top of the copper water pipe (from pump to head) looks a bit dried but seems to be okay. I'm going to replace it. (I can't believe this small rubber grommet goes for about $20 no matter where you look). Anyway, I still don't have any clues as to why it's overheating. Anybody familiar with these single cylinder 2 horse motors? thanks

 

[Daviet]

Re: 71 johnson 2 horse overheating

As nwcove suggested, the head gasket could be allowing the compression from the cylinder into the cooling system, the water pump would not be strong enough to over come it and the engine would overheat.

 

[twocyclemania]

Re: 71 johnson 2 horse overheating

If it's the head gasket would I find water on the spark plug or inside the head?

 

[Daviet]

Re: 71 johnson 2 horse overheating

Not always, the piston can push compression past a defective head gasket into the cooling system pressurizing the cooling system, but water will not flow into the cylinder.

 

[angelo1369]

Re: 71 johnson 2 horse overheating

a small leak could allow compression into the cooling system without showing water on the spark plug. A compression test is the best way to tell.