Is it a full on backfire or just a bit of popping. You may want to check the exhaust seals for any air leaks, this can cause some popping and banging. Start with the basics, check the plugs, ht leads. It could also be that the bike is running too lean, a fuel/tuning issue. Have you got an aftermarket exhaust on? Do you know what air filter it's got? Check the air filter is clean.
You say it's been cutting out. What's the idle speed set at, It should be at 1200rpm ish but you can up that to 1400 and see how it goes. For the idle speed adjustment there is a black knob on the front carb, on the right hand side through the triangular part of frame behind the rad. Turn this one way or another to increase or decrease the idle speed.
Hope that gives you some direction to go in.
(:-})