I bought a 05 brute 750 off of an older fella. He said he was riding it along just fine and then it just started running rough midride. He let it go cheap because he couldn't figure out what was wrong with it. It starts fine and idles decent, little popping through the carbs. When you give it throttle it starts backfiring and popping through the exhaust and carbs. It won't go above 15mph and has no power. The exhaust also gets hotter than hell in less than a minute. I replaced the plugs. Pulled the carbs and cleaned them several times hoping I had missed something. I adjusted the valves. Eliminated the buss connector, and made sure it isn't in limp mode. Any ideas on what I'm missing or what it might be?