90 Mercury 40HP motor

[warddog]

Bought a 20 ft pontoon to use on our pit and it came with this 40 HP motor. It is a 1990 Merc. 40HP, ELPTO, 4 cylinders with a serial number of OC226261. It is oil injected. Pulled it off as it is too big for our use and decided to have it checked out at the local marina due to having sat for approx. 12 years or so. They checked it for compression, fuel and fire with the results saying it had compression of #1=120, #2=120, #3=110 and #4=95. #3 and #4 have scored cylinders. It also had no fire and a horn going off. I don't know what No FIRE and a horn going off may be but do know that scored cylinders would mean, tearing it down. I have wrenched on a LOT of stuff but never an outboard motor and I figured this was enough to not be worth putting any money into and curious if my thoughts were correct? I do have the service manual for it. I brought it home and figure I may just part it out.

 

[Chris1956]

You might stick a bore scope into the bottom two cylinders and see if the cylinders are scored, or if the rings are stuck. Sometimes when motors sit for a long time, the rings stick. Sticky rings can be loosened w/o disassembly.

Not that I don't trust the shop, they may have been too busy (lazy) to check it.

As for the spark, you might check the condition of the wiring harness. Merc has issues with the harnesses going bad and the insulation falling off. I would think this issue was fixed by 1990, but That motor is an older design, so who knows.

 

[racerone]

Remove lower bypass cover and inspect pistons / rings.

 

[Texasmark]

Before you go to a lot of trouble, get some Sea Foam (auto parts stores have it) and put 2 oz. per gallon in your fuel tank in addition to any pre-mix requirement. Run the engine till that tank of gas is gone. If you still have a problem, then "I" would start looking into engine problems requiring things to be removed and inspected. I just have the motto: Don't fix it if it "ain't broke!". My experience over the years is that it has saved me a lot of fooling with stuff that was acting up but not "broke".

 

[airshot]

I have a 1992 version of that motor and love it. Been one of the best running motors I have ever owned. Whether your's is worth putting money into it, is your call, but ....from all that I researched before buying mine, they were great, reliable motors. Smooth idle, so slow you can hear each cylinder fire and mine will outrun any other 40 up I have owned and I have owned quite a few.