Lack of RPMs Yamaha 40HP 2 Stroke

Dadnova

Recruit
Joined
Apr 10, 2020
Messages
4
I have a Yamaha 40HP 2 stroke that I cannot get above 4700 rpms. Its a outboard jet drive, timing is dead on, and played with, no differance, no miss fires, carbs gone through, again and again, everything OMES out good. Air screws in more or out more, same thing. One puzzle I cannot solve.
 

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
8,851
seems the other tread states the jet lower will not allow the RPMs to reach 5500 due to the load put on the motor.

do you have proof that those 40hp power heads will run 5500 with the jet lower on it?
if so post up what you have
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
While solo boating try testing the motor at wot at different transom heights, for that need to install and induction tach to check the wot rpm differences gained at different heights. Compared to an outboard motor the more load you go boating with can be compensated with less pitched props to run towards max wot rpm range, on jet drive motors you can't so will need to play with motor/transom heights and the least load on board for motor to rev to at least middle of its wot rpm range.

Happy Boating
 
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