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I recently bought a fishing boat with a 1985 90hp. Without ntaking it to the Lake to run it, I hooked it up to the water ears..seemed to run out fine. When I took it to the Lake, I couldn't get it to reach any kind of decent RPM's. I took it home, hooked it back up to the water ears, and it seemed to run out fine?? I pulled the plugs and ran a compression test on it. 80-70-80. I haven't bought a manual yet so I'm not sure what the compression should be...seemed a little low to me. When I had it on the Lake, I trimmed it up out of the water for a few seconds, and the RPM's came up..as soon as I put it back down in the water...lost the RPM's. Any Ideas?? Thanks...I'm new, this is my first post.
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Spitfire,
If that 90 Yammie has not been de-carbed in the last two years, I would do a shock treatment with Seafoam. Scroll down thru the posts where I describe the procedure. This will clean up the carbs a little, and de-carb the pistons and rings, and maybe bring up the compression a little.
You probably have gummed/varnished carbs - if the shock treatment does not help, try removing the needles of the jets and squirting Berryman's Chemtool into the seats - make note how many turns the needles are before removal on the low speed jets.
If removal and cleaning of the needles and seats of the jets doesn't help, then a carb overhaul is probably in order.
Good luck,
Ken K -
Ken,
As you may remember I just had my carbs rebuilt and I am still trying to educate myself as much as possible to avoid future problems.
How difficult is it to "remove the needles of the jets" as you describe here? Would I have to tae the carbs out? Or can I just access the needles of the jets with the carbs in place? I have a Clymer's manual for my engine but it doesn't have the greatest pictures on this subject and that was why I didn't trust myself to re-build the carbs. Thanks.Comment
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rmart,
My Yamaha manual refers to the jets on my C115 carbs as "main jets" and "pilot jets" on each of the two carbs. Mine are accessable without removing the carbs. Yours may be different - you really need a Yamaha manual to go with that Clymer's - also, you could go and look up your model Yamaha on the parts diagram at boats.net, sponsor of this forum, to see where the jets are located.
Good luck,
Ken KComment
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Rmart, in our 90's the pilot jets and the main jets are located inside the float bowl. The only way to get to them is by disassembling the float bowl from the mixing chamber. The only screw we can get to without removing the carbs is the pilot screw.Comment
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Maybe this is a dumb question, but everyone here as been so helpful so I will ask anyways, when one is having an idle problem is that a main jet or a pilot jet problem? What is the difference between the 2?Comment
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rmart,
I know it is very confusing - even my Yamaha manual seems to be confused on what to call the jets.
The main jet meters fuel for med-high speed operation. The idle jet, or pilot jet, meters fuel for low-med speed. The only one that is adjustable is the pilot screw that adjusts the fuel/air mixture for low speed. On my C115, the proper setting for the pilot screw is 1&1/4 turns out. For your 90, it may be a little different - that's why you need a Yamaha manual.
Since you can't get to the jets, according to CLL, on your 90 hp, then you will need to remove the carbs and install a carb kit if the Seafoam shock treatment does not fix your problem.
Good luck,
Ken KComment
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Ken, thanks for the info again. My engine is a 1987 115hp and my carbs were just rebuilt after some terrible idling problems. The engine is running like a gem now but I am trying to learn more from this site on how to avoid future problems and how to clean the 2 jets if the need arises in the future. I plan on running a SeaFoam shock treatment by filling my water separator at least once per year (including one more time when my season ends here in the Northeast).Comment
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rmart,
I think if you do a shock treatment with Seafoam once a year and run Seafoam in the main tank, one can for 16 gallons of fuel, every third or fourth 16 gallons, those carbs should stay pretty clean - as long as you don't let the motor set up for months at a time w/o being run. That's the hardest thing a person can do to his internal combustion engine, especially one that is carbed.
I try to run my C115 at least once a week in the off season - usually on the driveway with the earmuffs and garden hose - sometimes I launch the boat in the river so that I can run WOT and clean out the high speed jets.
If you can't run the motor in the off season, then follow the owners manual for storage - engine fogging, sta-bil in fuel tank, etc.
Good luck,
Ken KComment
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