Proper procedure for doing a compression test on a Johnson outboard?

[Jeff2012]

Hope someone can offer advice on how to get an accurate reading for a compression test on a Johnson Outboard?
What should a 1984 Johnson 140 HP be at when new and what would be acceptable now seeing as it is 28 years old?
Thanks
Oh yes, also, where is the coil wire so the motor doesn't start while testing?

 

[emoney]

Re: Proper procedure for doing a compression test on a Johnson outboard?

Jeff, I had a 1980 Evinrude 140 (should NOT have sold that boat last year...sheesh) and using a cheapo tester picked up for Harbor Freight mine ran in the 120 range. Someone smarter than me will come along and answer your questions in detail, especially about what originally would've been compression. As for "how to"; simply screw the tester into each individual spark plug spot and turn the engine over for maybe 3-4 seconds. Have someone help you so you can watch the test while that person is turning the key. Once the needle stops going "up", that highest # is compression on that specific cylinder. Make note of each one's number and as long as they're within 10% of each other, then compression is fine. Ex; #1 = 120, #2 115, #3 = 118, #4 = 121 and so on and so forth.

Loved my 140. She liked the fuel, but man that was a dependable engine that I still miss.

 

[metriccrescentwrench]

Re: Proper procedure for doing a compression test on a Johnson outboard?

I'd add that it would be a good idea to pull all the spark plugs (so the starter can spin the engine easier), and to disable the ignition (you don't want any surprises by lighting up the air/fuel mixture being spit out of a spark plug hole) by pulling the kill switch lanyard. Also, you'll get a stable reading faster if you can open up the throttle butterflies.

And yes, I'd think 120ish also, my '81 Johnson 90 is in that ballpark.