Hi I have a mercruiser 5.0 MPI that suddenly won't start. It's always been very good and starts immediately. It will turn over, and over and over, but never fires up. I can crank on it for a bit and then a "puff" of air, no odor, no color, comes out of the flame arrestor/air filter. I've tried giving it some throttle but same results. I tried switching out the IAC from the other motor which runs fine, but same results. I even put IAC from non starting motor on running motor and it cranked right up so it's not the IAC.