Engine surging

Zeeman

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Was out on the lake today and when I tried to accelerate to 5000 rpm my engine surged to 6500. I immediately backed it down to 4000 rpm and it did it on its own again and I had to throttle back to 3000 rpm. It was moving the boat ok but I have noticed I have been losing some speed this season. I have a 90 hp Yamaha. Any ideas what could be causing this? Spun hub? The trim was all the way down too
 
Engine surge sounds like a fuel or throttle cable issue. I would check the cable first to male sure everything is clipped and connected properly.

After that look into fuel issues - filters and water separators, bad fuel, fuel pumps etc. It's probably going to be a lot of guesswork but make sure all the maintenance items are up to snuff and performed properly before throwing parts at it.

Good luck!
 
Yup was also going to say fuel issue. Water in the fuel, fuel/water separator needs to be changed etc etc. . .
 
What year? Warranty?
 
Thanks for the replies guys, it sucks because I have babied that engine since birth
It’s tough when you take extra good care of the boat, and something goes sideways, or others cause issues/damages. I hope the good advice above, whether through your own efforts, or dealership/warranty if need be, get it resolved sooner rather than later.
 
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A fuel or throttle cable issue seems reasonable.
So - newbie question: How would a failing fuel pump, fuel separator or fuel issue cause speed surge from an otherwise normal speed? I would think those items would cause bogging or loss of speed? Appreciate the education, as always - so much to learn...LOL.
 
A fuel or throttle cable issue seems reasonable.
So - newbie question: How would a failing fuel pump, fuel separator or fuel issue cause speed surge from an otherwise normal speed? I would think those items would cause bogging or loss of speed? Appreciate the education, as always - so much to learn...LOL.
My thoughts exactly.
 
Check fuel line as well to make sure it's not getting pinched as speed or trimmed up.
 
Your guess of a spun hub sounds more like it. If the prop shaft or the prop has a full grip on the water you would need excessive power to achieve excessive engine speed (6500rpm). A potential problem source that limits power would result in less engine speed. Instead you have a engine speed that tells me your rev limiter is kicking in. Sounds to me that your prop shaft is not getting a grip on the prop or your prop is not getting a grip on the water. Tell us what you find out.
 
A fuel or throttle cable issue seems reasonable.
So - newbie question: How would a failing fuel pump, fuel separator or fuel issue cause speed surge from an otherwise normal speed? I would think those items would cause bogging or loss of speed? Appreciate the education, as always - so much to learn...LOL.

Generally yes but if you're WOT on the throttle and it's bogging and surging from fuel it could run up or down.
 
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