how to test compression

[dstroud1987]

hey guys,

I have been on here the last few weeks asking about some problems i was having with my 1962 johnson 40hp outboard. After getting a lot of good advise here, me and a friend checked everything and adjusted everything this weekend and now its back to running great out on the water. The funny thing is that after all the stuff i did.. i never once checked the compression. I know that would usually be the first place you start when troubleshooting a poorly running motor.. but i didnt have a compression tester and didnt want to buy one to use it just once.

Well finally a guy from work brought one in today for me to borrow, so i figured even though its running great, I'll check out the compression just for curiosity sake.

I have never done this before, and im sure this question has been posted before, but i just love bugging you guys all the time lol

So is it as simple as un-hooking the fuel line and taking out the spark plug then screwing in the compression tester and turn it over with the key (electric start) a few times until the gage stops going up?

and do i leave the second spark plug in while testing the first one?

I know these questions seem kind of stupid, I just like to know what im getting into, and you guys are great with letting me know things that i would have otherwise overlooked.

any advise is appreciated as always!

 

[JB]

Re: how to test compression

http://forums.iboats.com/showthread.php?t=313963&highlight=compression

 

[86 century]

Re: how to test compression

All plugs out. Plug wire securely grounded or disable ignition. Crank her till the gauge stops climbing.


Some will say eng needs to be warn with throttle wide open for the test. My thoughts have all ways been test it cold then warm with throttle in both positions.

Its yours so why not know what you have its not costing you anything.

 

[lindy46]

Re: how to test compression

As long as it has gas in it, I'd disable the spark by grounding the two wires going to the "M" terminals of the ignition switch. Don't want to start a fire. Or run ALL the gas out of the motor before testing.