How to do a compression check

[oakcenter]

I want to check the compression on my '66 Evinrude 80hp Starflite. Can anyone tell me the correct way to go about this?

 

[racerone]

Remove 4 sparkplugs , install tester.----Crank over till gauge stops rising.-----Throttle does NOT need to be open.

 

[oakcenter]

Thanks Racerone. What is a good compression number and when should I be concerned not high enough? I've seen different posts about the differences between each cylinder. How far apart can they be?

 

[racerone]

????--------Just post your values after testing.

 

[oakcenter]

If I can find someone to help me I will.

 

[Boobie]

OMC says not more than 15psi variation per cylinder.

 

[oakcenter]

Got 90 on all 4. Is that ok?

 

[oakcenter]

When we did the compression check we removed all 4 plugs and checked each cylinder. Battery was fully charged. The engine would crank hard and slow. Is this how it's suppose to be or should it crank faster like it does when the plugs are installed?

 

[fdrgator]

Normally, it would crank slower with plugs installed. But "lumpier" with all out except the compression tester. Either way, it has to crank it over the compression strokes.

 

[oakcenter]

It cranks harder with all plugs out and compression tester in one cylinder. Is this a sign of more problems?

 

[Boobie]

It's normal............