OK, this is my first Yamaha (I'm a Polaris guy). Just picked up the above quad - runs pretty good except for a very noticable stumble *just* off idle. If I hold the throttle open just a tad it will stumble indefinitely. I get rough power again a about 3/4 and at WOT throttle is runs pretty good I guess (I have nothing to compare it to) but it seems like it may be lacking a little smoothness there too.

I read here that adjusting the valves may be in order? Could that cause the problem, or am I more likely looking at a carb problem?

 

Wow, nobody has anything? I checked the valves last night - exhaust was within spec, intake was no measurable gap at all - so I gapped it to between .004 and .005 in.. No difference.

It's definitely a stumble at high rpm - it just can't hold full speed above 3/4 throttle and seems worse once it warms up. I'm thinking the carb is in sad shape. The prior owner said it sat for about a year.

Come on, can't anyone offer anything? Don't give me a bad Yamaha experience to begin.

 

Geez. Way to ignore the new guy.

I never got ignored on the Polaris forum. I got more answers to this issue on my Camaro forum.

 

Then go to the Polaris forum and ask them [img]i/expressions/face-icon-small-wink.gif[/img]


MAybe nobody has a breeze? OR would only suggest what you have already suggested...valves or carb.

Good luck.

 

If it sat for a year I would clean the carb and gas tank out for sure, you may have moisture in them. Also old gas can gum up and clog jets, the best thing to do is clean it really well, (make sure it has good spark)get a new spark plug(gap it too), and see how that works for you.

 

I have a Breeze and it "did" the same thing. Stumble right off of idel. My daughter even talked about it.

Finally had time to look at it. Took the carb apart and looked at things.

The cure?

I put a small washer under the main jet needle (shimed the needle.) Boom, end of problem. Someone said they had a clip type of needle but not on mine? If you have a clip, lower the clip 1 or 2 positions. You "might" even have to go up 1 size on the main jet?

 

<div class="FTQUOTE"><begin quote>Originally posted by: Doctorturbo

I put a small washer under the main jet needle (shimed the needle.) Boom, end of problem. Someone said they had a clip type of needle but not on mine? If you have a clip, lower the clip 1 or 2 positions. You "might" even have to go up 1 size on the main jet?</end quote></div>

Thanks Doc. So you effectively kept the needle from fully seating?

I pulled the carb and found an 85 main jet - stock is 77.5 - and it is an all stock machine. I think that explains my high end stumble - its probably loaded up with fuel - who knows why the prior owner went to 85.

I called 5 Yamaha dealers and nobody has a 77.5 main jet. They had to order it and it is a week for turnaround - a little disappointing having to wait that long.

Don't know if that will fix the low end stumble too, but thx for the idea.