Got my Manual Today..still need help

[Spitfire]

Hi all, I got my Clymers manual today, went looking for acceptable compression test results for my 1985 90HP..but no help. It says..most important is that the results are within 10% of each other...Mine are...but, is the compression where it should be! Mine is 80-70-80. Do any of you happen to have a reference with compression numbers?? Thanks. Mike from Hotr-N-Hell Utah.

[boats.net]

Normally the 90hp runs over 90lbs compression. You might try a different compression gauge and check it when engine is cold and open throttle up when cranking over.

[Spitfire]

Thanks, I'll give that a try.
P.S. I did a wet test on it also...there was no change in compression numbers..I'm assuming rings are OK...could this be a head gasket problem??

[Ken]

Spitfire,
If it has been at least three years since that motor was de-carbed, I would do a shock treatment with Seafoam. That just might loosen up those rings a bit and bring up the compression.
Good luck,
Ken K

[Terry]

Please let us know how this goes and the results you get. I'm getting ready to do my own carb r&r on the same rig. (1988 90HP)

I'm waiting on gaskets & parts, including new reed valves. (don't know that the old ones are bad, but I thought I'd give a set of Boyesen reeds a try "while I'm in there.") I'm doing a refresh on the carbs & reeds to start with. Probably finish off the season and then pull the exhaust covers & head and see what I have.

I'm also looking at lower compression numbers, but not as low as yours. (95, 95, 100). We may be fighting similar battles. Mine still runs pretty good, just doesn't pull a lot of RPM's on top end like I think it should. (4700 on 13.25x17 AL prop, 16' all-purpose ski type boat). Comparable rigs with same motor & prop seem to pull 5500.

FWIW, I've been impressed with the SELOC manual I bought, but both the SELOC and the factory Yammie manual do not specify compression numbers, only differences between the jugs.

I did the Ring Free shock treatment with a couple of spray cans of Yamaha combustion chamber cleaner. Lots of smoke, noise, and smell. Before: 95, 95, 100. After: 95, 95, 100. Flashlight in sparkplug hole revealed that I could "read" the markings on top of the pistons. I don't think I had a carbon problem in the first place.

[Spitfire]

I completely disassembled the carbs, cleaned thouroughly with Chemtool.Put back on..ran the "Seafoam" flush as Ken described..couldn't tell a diiference (Dang it!) Ran new compression teste..changed a little from the first time...now 80-90-80. After running it for quite some time..I pulled the plugs to check them out...all 3 are semi wet..Could this be a low compression problem?? Carb problems?? I'm willing to try anything! Thanks for all your advice Ken.

[Ken]

Mike,
Well, the compression did come up on that middle cylinder from 70 to 90 - but understand doing a shock treatment with Seafoam or any other detergent is not a cure-all.
Your outboard is 20 years old, and the rings are probably worn quite a bit. How does it run now on the lake? What is your max rpm up on plane and trimmed out? What is the approx weight of the boat? What is your max speed? Have you put in new spark plugs? Give some info on the actual performance.
Ken K