Last summer, I changed props due to damage on the old one and when I did, I dropped the pitch and went up in diameter. I'm not 100% sure what prop I went up to, but I think it was a ACME 497, I will have to look at next time I go up to where it is stored. Any way, the next time we were out on the water, the engine had developed a miss and it would backfire from time to time at cruise. I tried to duplicate this problem out of the water but it does fine on the fake a lake. It seems to only do it with the boat under way with its own resistance. I haven't changed the cap, rotor, or spark plugs in the last two years, I was going to probably start there, but I was wondering if any of you guys had heard of this before and see what else you think it might be? Any input is greatly appreciated. Thanks guys.