For what it's worth, the factory break-in specs for my Seidel 770 (green card) were 5,250 rpm high speed and 1,350 rpm idle on a 24x8 prop. For the 990 on a 24x10 prop, the specs were 5,100 rpm high speed and 1,400 rpm idle. Not sure they mean anything more than the engine will run, as they seem pretty close for an extra two jugs.