My 700 xtx was doing the same thing only in water. It would idle fine and run low rpm but when you would get in to it hard it would miss and back fire. I checked my coil and found the way it was bolted on it was mashing the spark plug wire up against the mounting plate, i took it off and coated it with liquid tape about 4 coats and shimmed it away from the mounting plate about a 1/4". I have not had a chance to ride in the water yet but have noticed it starts easier and seems to run better.
2009 700 xtx
alum skid plates (fabrication by me)
rear bumper (fabrication by me)
front brush gard (fabrication by me)
crow harnes (4 point)
lower tail light
epi clutch kit
full wind sheild
e brake alarm (utv crap)
sound proof engine cover
trail armor doors
rear sound bar
stage 1,2&3 clutch work by ///AIRDAM
Stock roll cage lowered 3"