Battery connected Backwards

Hey everyone, i had battery off and charging, wife put it on while i was at work.She put wires on wrong side. She said it would just hum when she pressed starter. I fixed the wires and now I have an atv that misses, spits and sputters and backfires when you give it the gas. Its a 96' Polaris 425 magnum. What electrical damage could this do? All of the lights, power source, & starting components still work like normal. So which of the electrical components cause the engine response to be affected ????any help appreciated??????
Thanks, GH