Compression check procedures

[Rick.]

Hello. What is the correct procedure in doing a compression check on a 1971 Evinrude 4 HP? Do I remove both plugs at the start? Does the engine have to be warmed up? This motor has sat for some years but I cleaned it up, oiled the cylinders, and started it up two weeks ago. It ran very smooth at idle. Thanks, Rick.

 

[Sherman]

Re: Compression check procedures

You have it right, warm up then take out both plugs run compression test. Cyl. need to be within 10 percent.

 

[tashasdaddy]

Re: Compression check procedures

it is a rope pull motor, so pull the rope until the compression guage quits going up. then pull the same number of time on the other cylinder. that is a great motor and easy to work on.

 

[Rick.]

Re: Compression check procedures

I checked the compression cold. Top and bottom were right at 85 each. Warmed it up and top read 89 and bottom was at 95. Are these good numbers? I'm still planning on doing a decarb as soon as I find time to get it on the water. Thanks, Rick.

 

[jeff_smith_0423]

Re: Compression check procedures

Not sure what "ideal" is on that motor, but you're within 10%, so that's good. You may get them more even after a decarb, but if it's running good, go with it!

You can modify the decarb procedure and do it in a barrel - just skip the WOT step and run it at 1500 rpm or so for a few minutes. Just keep an eye on it and don't let it runaway.