4 HP Johnson uneven compression

[Bitmess]

I'm looking at a 1976 Johnson 4HP 4R76M.
It has pull start only.
I didn't warm the motor up and didn't put it full throttle because I didn't know I should.
The top cylinder has 60 psi
The bottom one has 90 psi
It will crank up and run in a bucket. It took about 6 pulls to get it started.
The seller says it's been sitting up for a long time. He rebuilt the carb and water pump.
Should I bother to look at it anymore?
Thanks

 

[Rick.]

Re: 4 HP Johnson uneven compression

I would suggest you pull the head and look at the gasket and head for possible leaks. 90 is very good for a rope pull but a difference of 30 is not good. Unless your a risk taker you may want to pass on it but I think it could be just the head gasket which would be a fairly cheap fix if your doing the work yourself. Best of luck with your decision. Rick.

 

[tashasdaddy]

Re: 4 HP Johnson uneven compression

i would invest $10.00 in some seafoam and do a decarb on it. it could free up a stuck ring.

Decarb, take a can of seafoam put 3/4 of it in the gas tank, with only 1 gallon of premixed gas. put the rest in a spray bottle. start the engine, and let it come up to temperature. then remove plugs, and them some real good shot of seafoam into the cylinders, replace plugs, let sit 15 minutes. restart, and spray the rest of the seafoam into the carbs, so the the motor almost stalls, wait and repeat until the seafoam is gone.then take for a wide open spin. then put in new plugs, ad premixed gas to the tank, and take it for a wide open throttle spin. it is going to smoke like a house on fire, during this process.

afterwards compression.recheck