[icknick]

I did a Compression test on my 1986 Mariner 150 HP and didn't get back very good results. I just need to know if I have to rebuilt my motor or what.
the results are as followed

80 100
120 110
115 115

that 80 is really bothering me is it really that bad? Thanks for the help.

[renny1]

if you read my thread you will see i am a complete newbie with outboards....my compression was 120 in 5 pots and 30 in 1 ended up being a broken ring(strip down) but with yours being 80 try de-carbing you may be luckier than me,but a strip down isnt as bad as it seems

[j_martin]

What does the plug from the bad hole look like?

[icknick]

Hey guys sorry about not replying it's going to be a busy week for me at work I should be able to take a look at it this weekend. I'm a complete newbie but I do have the manual.

How can de-carbing help with the compression?
Also j_martin what do you mean by the hole? the cylinder?

Thanks

[j_martin]

yep, the cylinder. What color and deposits are on the spark plug could give you a clue to what's going on without taking off the head.

If a ring is stuck in the piston, it could degrade the compression. If it comes loose with a little penetrating action it could help. De-carbing fluids, like Sea-Foam, Power-tune, etc are basically penetrating oils and solvents. The readings all over the board suggest stuck rings.

If there's aluminum on the plug, yer in deep doo-doo. Likewise if you peek in the spark plug hole and it looks like someone went to town with a chipping hammer on the piston. If the plug looks like it's steam cleaned, ya got a bad head gasket, and so forth.

Post a good close up sharply focussed picture of the plug.

hope it helps
John