Jet boats are under load at 3300 rpm ....... My guess is that it probably does need to be 13:1/ 13.5:1 for better power
Ok, I'm going to stir the pot some here. If the motor is already spinning 3300 rpm with a "lean" fuel mixture, why would you want to richen the mixture for better power? The extra fuel will just be a waste. The motor may be capable of more power at 3300 rpm, but the load on the motor will remain the same unless you go to a bigger impeller.
Nubbs (just stirrin the pot some)