1989 Johnson 70hp Compression results

[svranjic]

Just managed to borrow a mates compression gauge. It was just a hand held one, one that u push on whilst cranking the outboard.

Test was done cold

Results:

Top cylinder 130psi

Middle cylinder 126psi

Bottom cylinder 123psi

Should I be happy with these results?

Also wondering if I should do a Decarb on the motor?

Cheers

[BaitThrower]

Yep they are ok results... As long as all readings are within 10% of each other, thats considered a succesful test... Yours are only 7PSI max from lowest to highest which is good... Those figures seem good too. I wouldn't be worried.

[FNQCairns]

I would do a decarb because it's cheap and you just never know, then check again after the next run with the same guage and compare. The coldest cylinder often is the lowest one on 3cyl engines...colder = more carbon, yours looks basically like this but still just like global warming it could all be easily explained as natural variation.

Consider the mec power tune, it does actually soften the carbon well in a little test I did a while ago, better than each of the other brands I tried side by side.

cheers fnq

[BaitThrower]

I used OMC Engine Tuner decarb spray on my Johnson 15 (now gone) a while back and it produced good results.

[mercury'srising]

Now you got it. Those compression readings are OK. Now you know where it's at do it after every few uses. This is the best indicator for any outboard especially 2 strokes. Also, I meant to tell you on previous thread to inspect the plugs for water damage regularly. A sure sign of water entering a cylinder will show up as tiny pit marks on the plug surface or electrode. If you do regular checks for this quite often a major hicup can be avoided. Make sure you put the plugs back in the same holes each time. FNQ is right, the Merc one is better, just don't drown it when you do it. Keep up the checks and maintenance and you,re on you way to good boating.
HEY< You should have a few bucks saved from expensive servicing now.
Time to top up the tackle box EH ?

MERCURY'S RISING WHILE OTHERS FALL !