carbs......
First, why are your needles in the top notch?? if it's a 750 with amals, it should be in the middle groove... and you should put it there so you have a known point of reference to work from. IF,....... later you have a rich mixture in your midrange and want to try the top groove then that would make sense, but start out with the recommended settings so you havea frame of reference to start with.
Next, the fact that it pops and backfires at low RPM, but then comes on strong when you open the throttle sounds like you have a clogged idle ciruit. If you've cleaned it out recently, iike maybe with a toothpick, then you know it's clogged now... I like to use a sewing needle because it won't leave behind any shards of material when you poke the idle jet. A toothpick is the worst thing you could use. It will clog the idle jet if you poke it with toothpick.
Needless to say, you need to make sure your timing is correct, and since you can get your bike up to 5000 rpms, you should put a timing light on it and make sure your timing is good. Sometimes the magnetic rotor that fires the timing pick ups for the boyer ignition slips on the camshaft so it messes up the timing... A timing light check will tell you if that has happened.
AV gas... I used to be part of a dirt race car team and would mix half 108 leaded race car gas with half pump gas and my bike loved it probably because of the cooling effect of the extra octane and cushioning effect of the lead on the valve train. What is AV gas's octane rating? is it also leaded?
