I agree with Jethro as well. But back fires can be caused by a lean condition as well. What condition are the plugs in? Wet and oily or dry & burnt?
Either way I suggest you pull the carbs make sure they are definately clean after the long storage. Could be as simple as a plugged jet, allowing the air to gas ratio to be to high & pre ignition, and BOOM, back fire.
Sorry but I have too....
skidoo_magoo, this is a HELP forum for Polaris. Take your opinions of what is best to the General forum. All 30 of your posts have been verbal vomit just to hear yourself talk. When your daddy stops fixing/buying your toys your gonna need help, I for one will laugh & point at you. Grow up, post something constructive or don't post at all!
skidoo_magoo congrats you just made my ignor user list!