The backfiring would indicate a potential problem with the air cut off valves. They enrich the mixture on deceleration to prevent backfiring. As far as adjust the idle mixture screws I don't know how it can be done without one of these. http://www.bikebandit.com/product/1780Hurray! I just balanced the carbs... Lots of power now and I just got 35pmg! Much better!. It still backfires a little sometimes, so it still needs some tweeking I think. The lowspeed mixture screw is a real pain to get to- any hints on setting this better? I can just barely get my hand in there but the intakes and stuff get HOT! I cant get a needlenose in there and I don't see how to even get an offset screwdriver in there. I'd like to adjust them correctly and then rebalance them.
Thanks for the suggestions on the neutral switch, but it really looks aweful to change right now, so it'll have to wait till the carbs are adjusted better.