2004 Yamaha 150HP 4 Stroke

[Pancho390]

A Friend has the above motor that he can only get 5000 RPM's and 38 MPH running the lake.
The weird thing is when he's at a lower elevation, (just above sea level), he can get 50MPH and 5800 PRM's.
He's taken it to the marina where they changed the MAP sensor but it didn't change anything.
He's added gas treatment and changed the plugs with no change! He's pushing a Triton 19' boat.
Any help would be appreciated!
Thanks! ​

[clayshooter100]

What is the elevation where he is turning 5000 rpm?

[Pancho390]

Elevation of the lake is 2000'.

Thanks!

[SkeeterStew]

Had something similar and it was pinhole in the gas bulb. If he hasn't changed it in a year, it might be an easy, cheap fix.

[Pancho390]

Thanks!!

[Pancho390]

The lower elevation, where the boat runs great, is about 50' above sea level. It doesn't make sense??!!