Yamaha 90hp Rpm Problem

[Adventurer]

I have a 93 90HP yamaha outboard jet. The motor runs fine and all compression is good as well I have eliminated a fuel problem. When I open it up I can only get it to go to 3400 RPM's and this will not allow me to get up and going. Any ideas it almost seems like there is a high rpm shutdown holding it from going up to the required RPM.s

 

[jim dozier]

Re: Yamaha 90hp Rpm Problem

Verify that it is running on all cylinders. Do this by pulling spark plugs 1 at a time and check to see if one doesn't make any difference in the rpm range.

 

[Adventurer]

Re: Yamaha 90hp Rpm Problem

I have spark on all three cylinders.

 

[Fouled Plug]

Re: Yamaha 90hp Rpm Problem

Jimd meant to pull plug wires while it's running to see if all the cylinders are hitting. Another easy way to confirm this (with no risk of shock ) is by using an electrical test light. Ground the alligator clip, and push the probe into the spark plug boot while the engine is running. It will ground the plug lead. If the motor doesn't change RPM's, you've found a dead hole. Good luck!

 

[jim dozier]

Re: Yamaha 90hp Rpm Problem

Right, because you can have a dead cylinder due to fuel issues even if you have spark on all 3 cylinders. Another thing, my Suzuki oil injection will cut in a rev limiter if it thinks the oil injection flow is compromised, either by no oil, clogged filter, or gorked sensor. Check your manual, yo do have a manual right? See if there is such a thing on your Yamaha assuming this is a 2-stroke right?

 

[Adventurer]

Re: Yamaha 90hp Rpm Problem

Thanks for the help, I will pull the plug wires one at a time to see if this is the problem. Yes the yamaha does have a oil sensor, I have already eliminated that though. Thanks again for the tips I will let you know if this is the problem.