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Good morning Whaler Nation! I have a 1993 Montauk 17 with a new Yamaha F90 onboard. I had a painted aluminum 13x19 prop installed on it while waiting on my SS prop to be delivered. I got good performance at 5800 RPMs WOT. WOT range for Yamaha F90 is 5000-6000. Top speed was about 38 mph on the GPS.

At the 20 hour service I had the dealer install my new SS prop which is a Yamaha Performance Series GYT 3R 13.25x18. But now my max RPM is 5000 at WOT with a max speed of about 34 mph on the GPS.

The drop in top speed with a decrease in pitch makes sense but the 1” drop in pitch should not have dropped the WOT RPM by 800. Even with 1/4” larger diameter. If anything, the RPM should’ve increased with the drop in pitch right? I just don’t think I’m getting the max performance out of my new engine at 5000 RPMs WOT.

Or could there be a different issue created during the 20hr service? Fuel flow? I can’t think of anything. Other then the RPM drop the motor seems to be running flawlessly.

Thanks for any insight you can provide before I go back to the dealer!