Tim,
Most of Ivo's advice is probably relevant, however, backfiring through the carb is also a symptom of a lean mixture, I have an old 650 Yamaha which is very prone to this if I take the choke off too soon. Even if your carbs look clean on the outside, make sure you have good gas flow into the carb and that the jets are perfectly clean.
Most of the time, a bike which has been sitting a long time will have fuel system problems caused by rust and or varnish and often corrosion on the points.
Don't get too complicated until you try the simple things.
Ron