check this out i have been chasing my ass trying to fix a problem with my ski it just was not running right and i have to date changed elec box rebuilt my motor (ported while apart) tryed more compression bored my nozzel and i was just about to sell my prop thinking it just wasnt turning it but last night after changing my head to a different o ringed one and it blew the o ring out i put a straight edge across the barrel and it looks like this has been the problem for ages i will let you know in a couple of days if it was . hopefully now i own a ski that has more bottom than a 550 again