I have a 250 HPDI on a Ranger 521. Yamaha replaced the powerhead in Jan 2007.

I'm running a 25" T1 prop. When they replaced the powerhead, Yamaha tested the boat with a 25" and 27" and gave me a new 25" for free.

Ordinarily, the boat tops out at about 71mph (GPS) at 6000 RPMS. I can get the RPMS up to the limiter but speed doesn't improve. I've had a couple trips lately where ther RPMS run up to 6200 but my speed is stuck in the high 50's. But it doesn't happen every time. I took my mechanic out and that time it ran fine.

Any ideas what could be happening? All I can think of is 1) the prop is slipping or 2) something is wrong with my tach.

The motor is still under warranty but the dealer is an hour away. I thought I'd see if you all have ideas before I tow it to the dealer.

Thanks