How do you know if a RPM guage is correct.....cuz my boat, 1997 yamaha 150 hp pro V really only says it is running like 4900 with the hot foot pressed to the stop. I recently bought the boat, I would guess I can adjust the hot foot so the pedal pushes further....you think thats the problem?

The motor could be maxed out rpm wise with your current prop setup. You could try and hit the throttle under the hood or try adjusting the hot foot.

You would have to check it against another tach.  You can buy cheap one off ebay that the pick will just wrap around a plug wire, or if you know someone that has one that uses the reflective strips or the contact type you use that. 

 

You might want to pull the cover off the carbs and have someone mash the hot foot while you are looking at the butterflies in the carbs and make sure they are going fully horizontal.  Could be an adjustment or something hung behind the hotfoot.

thanks I will try to look at carb flaps

I agree with the prop issue.  It will make a big difference in the rpms.   Call Yamaha with the engine specs and they will tell you what pitch is recommended for that motor.    You will find the pitch transcribed on the prop cowling usually.

97 Yamaha 150's could be EFI or carbs, look and see as suggested. Throttle linkage would be the 1st place to start trouble shooting followed by checking the tach also suggested.

Tom