Love my Yamaha, but have a rough idle sometimes

[THerbert]

Hey all,

Hope you can help me with a intermittent rough idle problem. Yamaha 2010, 150hp 4 stroke. Normally you can't tell the thing is running, but a couple times per trip it will develope a rough idle (noisey and shakes). Dosen't seem to effect performance, no change in RPM or speed. Most times it's in the 6 MPH zones, low speed and sometimes in neutral. If I pull back on the throttles until its almost out of gear it straightens out. Had it to the dealer and he told me my prop was too large and was out of round, causing the shaking. I asked how that could explain the rough idle in neutral?? (looking for a new mechanic, that's another story).

Tim

[99yam40]

You may want to search and read Rodbolt17's posts on F150's to see if you can get any info out of them, he is a Yamaha Master Tech. and he has one of those himself and had to find a way to keep his from stalling at idle or just off idle
He has not posted lately, so I hope he will show back up on this forum.

I agree, hope you can find a Yamaha master tech or at least someone better than the one you used

[DeltaDawg]

If my motor is trimed all the way down so that it fully touches the bracket there is a certain RPM near idle that is the natural frequency of the hull and everything vibrates, triming the motor up slightly so it doesn't touch the bracket will break the frequency and vibration, is that what you are experiencing? If yes I wouldn't worry about it at all that is the way sound waves propagate. That's crazy a mechanic told you it could be the prop when you said the behavior occured in neutral when the prop isn't turning.

[THerbert]

Is Rodbolt back ? Ithought I seen a reply by him today. If so I would like to see his comment.

[99yam40]

Last post from him was 7/11/11 that I can find, you may have seen someone drag up an old thread that he posted on

[cruiser54]

hi,
just as a matter of interest, what prop are you using?
i have the same motor hp & year.
at very low speed r & f, but not in neutral i experienced engine "roughness" more like a metallic rattle that would go away over say 800 rpm.

this was diagnosed (by this forum) as prop chatter.
on investigation i had the wrong prop fitted, it was too "large/heavy".
it was a 17 K or T, being about a 14 3/4inch diametre.
i changed it to a 17M, i think it is 13 3/4 diametre, this fixed the rattle issue.

you may have the same issue but the noise also in neutral is a strange one?

cheers.