1994 40HP Evinrude Compression Difference

[phipps]

I found a 1994 Evinrude 40HP motor. I have not actually seen the motor, but the ad says that the top cylinder is 150psi and the lower is 125psi. I was thinking that ideally you would want the numbers closer together, but does 25psi difference make it a deal buster?

 

[HybridMX6]

Re: 1994 40HP Evinrude Compression Difference

Ideally you want them within 10% of each other, but 125 seems pretty high for that cylinder to be too bad off. I'd take my own gauge and a nice fresh battery with me and do one myself. Could have just been user error. If it's still lower, a simple decarb may take care of it if the rings are getting stuck up with carbon. 125psi just seems too high to be a major problem, unless it's just started.

 

[tashasdaddy]

Re: 1994 40HP Evinrude Compression Difference

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