Yammie taching vs. speed ??

I have a 2004 250 VMAX HPDI on a Legend 211 . This week I was up north on a lake that was smooth so I pushed the pedal to the floor . I was maxed out at a speed of 68mph But my tach was only reading 5400rpm. I also noted that when at idle speed my tach is at 600rpm.
Do these readings sound normal ? If so why can't I tach over 6000rpm's. I'm going to check my hot foot to see if it is adjusted correctly but other than that what can I do to get more rpm for more mpg's.

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Groma

You may be over propped and or motor too deep in the water. What prop and pitch do you have? 600 is a lil' low in neutral at idle. 700-760 is where mine is supposed to be. Your tach could be off as it is common. You could put a small prop on it and see where it reads when it hits the limiter. It should read 6150 or so.

I 'm running a 25 Ti VMax series prop. Should I try a 26 or 27 ? I there any way to check the tach or recalibrate it.

Groma

Thats how you can check the tach.... Run a 23p or smaller and see where the tach reads when it hits the limiter at 6150.... If it reads 6150 or close to it, The tach is accurate. The limiter is the calibrator.

If you cant turn a 25T1 but 5400.... You wont need any higher pitch props. Check for full pull on the throttle linkage by seeing if the throttle opens all the way with the motor cowling off.