anyone have this problem

ok i know its kinda the same thing over and over again........i got a 2008 Brute force 750 its back fireing out exhaust and in the airbox not a full throttle it does it when you let off its got a bunch of oil in the air box and the compression is fine, my dealer called kawie and they told them to check exhaust see if its cracked bc its been doing this sinced i owned it. i think its a lemon,, it all so had a new throttle body and tps replaced and a bunch of other stuff, is the 2009 and 2008 EFI systems the same can anyone give me a some idvice to suggest to the dealer.. Also they told me it might be valves might need adjusting you would of think they should of checked that since i brought it to them when the bike had 200 miles maybe. they wanted tro charge me to have them check my valves but i told them its been doing it since i owned it and i shouldnt have to pay for that am i in the wrong about that??? Thank you