Yamaha 90 Shaking

[Irish Hooker]

Hi all,
I have 2 1988 Yamaha 90's. three cylinder. One of them shakes when I have more than two people onboard. The rpm's go down form 3500 to maybe1700 then will go back up when the shaking stops. Giving it a little more throttle sometimes gets it to stop shaking.
Any thoughts?
thanks for looking
Matt
Irish Hooker

 

[Asainz320]

Re: Yamaha 90 Shaking

Have you checked for spark on all plugs? I think it could be that one of your sparkplugs is not firing.

 

[Ray Neudecker]

Re: Yamaha 90 Shaking

The only thing for sure based on your information is the motor is missing when it shakes. Check compression and fire first.

 

[BruceAML]

Re: Yamaha 90 Shaking

Does the motor have the correct spark plugs gapped and torques correctly? Does it have oil in the oil tank and is it pumping the correct amount of oil? Are the coils all good?