I let my buddy use my bike for a few days and when he got back it sounded like it was back fire every time that I let off the gas.. And it is loud. He claims he did'nt change anything. I am at a loss of ideas I have been through the carb atleast ten times.. HELP

try cleaning and reoiling your filter :excuseme:

Would you lend your girlfriend to your buddy? :bonk: I would not. :prof:

Read the plug and see if it is running rich or lean... rich black sooty plug, lean white center electrode... often when a motor is enrichened it will bark a bit louder than normal. I have found this to be true when tuning my old XL's.. until I get the carb needle position to a happy spot (usually the clip in the top notch on the needle) they will run okay but do as you describe and bark a bit - also they will not idle as smoothly and throttle response is poor and wisps of black smoke emit from the pipe when the throttle is blipped. This holds true for any carburated motor. Of course you may have an ignition problem too - but unlikely. Check the plug and go from there... also run 92 octane gas, my 2005 XR650L HATES 87 octane gas and will run but pops back alot.