Compression Test

[MANDINGO_1981]

What should my compression test readings be on a 1966 Evinrude Lark 40 HP Motor? I got 95 psi in both cylinders? Is that good? Thanks Carl

 

[jdsgrog]

Re: Compression Test

I believe what's more important is that the cylinders are within 10 percent of each other. As long as the compression isn't abnormally low. I have a '67 Johnson 33hp and I get about 110 psi in both cylinders, which to my understanding is good. I'm assuming from reading other threads 95 psi is alright and the motor should run. One thing that helped increase compression in my motor was a decarb.

 

[tashasdaddy]

Re: Compression Test

i would not be afraid of it on that motor. guages each read differently, as said when you get it running, do a decarb.

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