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Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 16209
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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My Yamaha 115 4 stroke races (rpm spikes momentarily causing

Customer Question

My Yamaha 115 4 stroke races (rpm spikes momentarily causing a lurch) between 2000-3200 rpm. You can see it on the tach and feel it as it lunges forward for less than a second. I have not noticed it at any other speed. What causes this? Prop slipping?
Submitted: 1 year ago.
Category: Boat
Expert:  Jason replied 1 year ago.

Hi Tom, my name is Jason.

It could be a prop issue but you said you changed it. Does it do the same thing with the new prop?

Does trimming fully down change anything?

Expert:  Jason replied 1 year ago.

Are you still with me Tom?

Customer: replied 1 year ago.
Sorry. I have been unable to open your response until now. I took the boat out this morning and could not get the motor to repeat the problem that I mentioned. As soon as it does I will test the trim. I first encountered the problem two year ago and changed the prop which did not seem to change much. It runs consistently fine over 3200 rpm. I usually have the spikes after cruising and returning to the dock. As soon as I lower the speed below 3000-3200 rpm I start getting the intermittent spikes. It does not yet pose a real problem but I am concerned if it is an engine problem that would grow worse if left alone.
Customer: replied 1 year ago.
I will take it out again later today and see if it happens again. Odd that it would do it frequently but not when you want it to!
Expert:  Jason replied 1 year ago.

Sounds good, let me know how you make out.

Expert:  Jason replied 1 year ago.

Hi Tom, how did you make out?