Help with 04' 225HP OX66.. loss of speed Skeeter ZX225

Been trying to figure out whats going on without taking it to the shop.. ZX225
04 225 Vmax OX66 Yamaha 27M prop
Boats speed has gone from 69- 72 depending on load to 55-56 MPH..
I know the heat will cause loss of a few RPM's and a few MPH but i think something is wrong..
Boat starts fine, idles fine, Holeshot is still pretty good but on top end it just doesnt seem to get there.. tach is still currently showing consistently 5800+ RPM..
in the spring i was 6000 RPM 70-74 MPH
Water Pressure still seems normal, engine sounds normal..
I've replaced fuel filter, the 3 fuel pumps on the side, cleaned plugs still in good shape
The prop does not appear to be slipping at all and everything looks as it always does...
Dont really know what to do and dont care to pay a shop huge amounts to diagnose the problem and dont want to cause any damage to motor if there is a problem.. please help


Modified by DerekG at 3:47 PM 8/22/2010

I know on my skeeter that I had, the hot foot pedal stop (the bolt) loosened and prevented the pedal from being depressed all the way down where it had been going before. Other than that, you going to have to wait on the smart people to show up.
britt

Well with it still getting to fairly high RPM's i'd think that it was getting the fuel.. will check though thanks

Dinged up prop? O2 sensor cleaning...

Prop was worked a little while back and is good condition.. it was dinged up more before i got it worked and speed was good then 70-74... same speed and performance after it was worked until now..
Dont have it B&B but all blades are ding free...'
have not cleaned the 02 sensor but will be doing it soon

hmm,, u got rpm's, shouldnt be fuel, maybe not even o2,,,,,
dont take this wrong, but is it triming up like it suppose too???
thats alot of speed to lose, with rpms

Yes it is trimming fine, boat is on plane with a tail as high as the cowling.. with this super hot water i'm going to drop the jackplate a bit and see if i can get any difference.. maybe prop is not biting good at higher speeds..
i'm going to clean O2 sensor tonight.. will update any results

You said you checked the prop but did you inspect it for stress cracks? I went thru 4 27ms in 6 years. Two of them lost blades and other two had stress cracks. Also, check the pad of the boat.

I will thoroughly inspect the prop this morning, i have checked the pad of the boat for any damage. other than some typical stump rubs its good..
thanks for the suggestions

I lowered the motor down to about 3 1/2 inches below pad.. now only pulling 5200 RPM at 60 mph... gain in speed but loss of RPM's..
My boat has run this set-up before and never had a problem getting RPM's up...
Checked prop, no cracks or fractures..
Had a compression test run.. all checks out OK with the bottom 2 cylinders being the lowest about 6lbs lower than the top 4 at 110..
Cleaned the 02 sensor- idles better
What now??

In my experience, loss of top end RPMs usually points to a dirty/bad O2 sensor. I saw that you cleaned it, but did you check it too? There's a link sticky on the top of the forum.

Thanks for the input guy's... got a brand new 02 sensor, put it in this afternoon and she run's like a top!! back up to 70mph @ 6000 RPM

Glad it was easy....running fast just in time for the long weekend!!