I just got this bike a couple weeks ago. Great Bike,

I ride winding mountain roads here in Colorado USA. the bike corners great and has excellent low end horse power.I'm getting backfire when I let off the gas, I'm not sure about how it should be jetted, I live in Evergreen 8,000ft. Elev. and ride to Golden 5,500ft. Elev., for work. Can anyone tell me if my backfire is a fuel-air mixture or jetting, or timing??
Trent in Colorado