The motor runs just fine at Idle but when I give it a little gas she misses and backfires through the exhaust and the carb. Its a 350 with a Holley carb. The guy I bought the boat from said that the motor was just rebuilt and that it doesn't even have 30 hrs on it. (AIR BOAT).If I gradually press the throttle to the floor it will sometimes miss and then rev way up. (Not all the time but some)Does anybody have any suggestions on whatcould be causing this to happen?Just want to get this thing runningperfect before I take it outin the marsh. I don't want to get stuck where nobody can reach me.lol Thanks

 

Possible cracked or wet distributor cap also could be plug wires leaking and cross firing. If it has a points typedistributor it could be in the points.
Backfire through the intake and exhaust both eliminates the possibility of a flat lobe on the camshaft.
I would check the tune up first then you might add a little marvel mystery oil into the fuel and engine oil incase its a problem of valves sticking.
If you do have a points style distributor I would be changing it out to electronic asap even if its a mallory or axcell dual point.

 

Check the timing...

 

^^ second that.....