Loss of top-out RPM, 2001 Yamaha VMax 225

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I have a 2001 Yamaha VMAX 225, 25 inch prop, on a Skeeter ZX 225. It used to top out at 5600-5700 RPMs--GPS 71 mph. Now tops out at only 5000-5200 RPMs--GPS 60 mph. Hole shot good! Hole shot RPMs 5400 then falls to 5000 RPMs. Have spent numerous amounts of money with area dealers, each professing to have fixed the problem. However, the problem still persist. Furthermore, making matters worse, motor is now producing a weird sound--unlike a motor knock sound, but a chuc-ha, chuc-ha, choo-choo sound. I have lost money and confidence with local dealers. I am hoping that somebody on this forum can provide information that will correct the RPM problem and noise problem.

Thanks,

Garry

[jb123]

1) have they / you checked, cleaned, tested the 02 sensor as those are the symtoms caused by a malfunctioning sensor.

2) have they/you checked/cleaned your HP fuel pump filter, as your motor could be starving for fuel at those high rpms.

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Jb123,

Have replaced 02 sensor and replaced fuel pump filter. Still same problem.

I appreciate your input addressing the problem.

Thanks,

Garry

[Ken]

Garry,
Has a compression test been done - if not, I would do it.
Good luck [img]smile.gif[/img] ,
Ken K

[jb123]

you replaced the HP fuel pump filter? they really only need to be cleaned....are you sure it was the vapor tank filter?
next you may want to run your motor, driveway, at maybe 1500 rpms, pull each plug and listen for a sound change to isolate the issue. then if you FEEL capable, pull each injector and listen for the sound change there.also has anyone pressure tested your fuel lines ??

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Ken and jb123,

First, thanks for taking the time to address mine and others problems.

Ken, my brother and I did a compression check last night--80 psi. for each cylinder. Is this the norm?

jb123, I am sure the 02 sensor was replaced, but am not sure about the fuel filter? I apologize in advance for my ignorance, but is there a difference between the HP fuel filter and the vapor tank filter. The filters replaced were located under the motor cowl. To my knowledge, fuel lines have not been pressure tested. Will do the pressure test and plug/injector routine next.

Thanks again for your inputs.

Garry

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jb123,

Just spoke with mechanic. The HP fuel filter and 02 sensor were replaced new. The VST filter was cleaned and replaced--would have replaced with new part but did not have one--and it really wasn't that dirty. Also, he pulled each plug but could not isolate the noise. He told me to be sure and stress that it is not a "knocking" sound but a "chuga..chuga" sound. The mechanic did not do a pressure test on fuel lines because he said if there were a leak, we would be able to smell the gas.

Thanks for current and future input.

Garry

[jb123]

80 sounds low but if they are all the same....hmmm wait for other input there.

the pressure test, as i gather, tests RESTRICTION of flow, ie pinched lines or other line restrictions, thus impeding fuel delivery, but you "should" see that in the clear filter. ive never done it or seen it but my tech suggested it after i replaced a powerhead.