This is on a Coleman Maxa 8500 generator. If choke is wide open, it accelerates, then lets off, backfiring, then accelerating again...continually repeating this with the RPM going up and down quickly. BUT IF the manual choke is then set to half closed, the engine smooths out, and runs steady. I have run a half of a can of SeaFoam thru it with no effect and no change to this condition. Its hard to believe the carb is gummed up after running so much SeaFoam thru it. The air cleaner/filter is clean & flowing well.

Jon Goodson, November 2007

Chances are you have water in the carb. Remove the float bowl and empty it. You might get away with just losening off the bowl nut. If that's not it, back out the high speed needle half a turn (if adjustable needles are fitted). If not adjustable, then if probably IS gummed up. You will have to strip and clean it.

One other possibility - VERY stale fuel will also do this.

Phil Saunders, November 2007