How much timing (Advance )do i add to the motor (sbc 350, only gas is 87 oct) ? It was set up for 2000 ft and now the boat will STAY at 6000 ft. Also, How many Carb jet sizes do I go down ? (thinking FOUR(4)) It's a holley vaccum secondary (no numbers available). I already got a new set of props(volvo) and the motors is running way fat and not much power. Max rpms is 4500 and thats wide open . The Boat will stay up at 6000 ft forever and will not leave the mountain. Thanks for the help.