1978 mercury 90 hp. HELP please

hi i have a 78 90hp tower of power..i have rebuilt all the carbs and replaced the impellar..i took it out last weekend and got it to idle and i think i need to fine tune the carbs...how do i know the sweet spot on those things so i dont burn a pistion? i race motocross and have rebuilt lots of 2 stroke carbs but this is a little different ball game lol any help would be greatly appreciated..this is my fist boat i just graduated high school and decided i wanted a boat. this motor is on a 1978 Del Magic Ski boat..its pretty sick. but if someone could give me a few pointers please that would be great..thanks!!

As told to me by a marine repairman, set then for 1 1/2 out and leave it go. He told me that some guys will tweak them a little, but in most cases 1.5 is the spot. I used to rebuild bike carbs too, YZ465, KX500, CR500 ... not too much different.

ok thanks man...