Cracking up

76 Kz 900 1075 kit kibble white stainless vailves 29 mm carbs are sinked. Dyna electronic ignition. The cracking up comes and goes between 3600 and 4500 when cruising. It also backfires but I have the proper jets and no air leaks. It seems to be lading up. When I go thru the gears it runs like a champ and also on the highway. I also cut one loop of of the advance spring because wears having alite problem with the idle. Any help please.

Hey Zap, could it be your timing advancer is not working right?

Check it out, clean it.....make sure it snaps back fully and that the springs are good.