i had a very simular problem with my hpdi. turned out to be very dirty filters combined with bad low pressure fuel pumps. i changed them all out and added a 10 micron fuel filter before the motor and never had a problem againhope this helps Chris
this is definitely a prop issue. with the motor trimmed down i am almost over reving. i am assuming that i should be able to trim to at least half way before my rpm start to get high.i think i need a 26 but i want to hear what other guys are running