Yamaha 115 4 stroks at idle speed in gear

[Billy Bones]

My problem is a 115hp Yamaha 4 stroke that vibrates at idle speed on a Tidewater 180cc. Thanks for all the feedback.
I now believe my problem is a boat problem. The boat has a 20" transom designed for a 90hp motor but with a 115hp maxiumhp recomendation. I think that on a 25" transom the 115hp would work fine. But the Mfg, the dealer and the Yamaha tech all disagree, so I just accept it. The motor runs great except at idle up to 1100 rpm.

 

[Texasmark]

Re: Yamaha 115 4 stroks at idle speed in gear

If you have a high pitch, heavy prop it could be natural. I have 4 props for my engine (totally different from yours) and the pitch varies from 17" to 24". The 24P is SS and has a lot of blade area, hence is heavy, bought it new from this site. When running it, at my lowest idle setting, (675 rpm in F gear in the water...per the manual) it runs rough.

Kick the rpm's up to 1100 and all is fine. Running with the lighter weight, lower pitch props, all is fine at any speed. I want to run the 24P so I just put up with the engine trying to push that much load with the cylinders firing as seldom as they do at that speed.

HTH,

Mark