guess its like any motor you can feel where its happy...i have no proplem at 2000 rpm on level road where im riding and warming the motor up at the same time ..once its warm 2500 seem about the norm if in a lazy mood.... buy my bike has no problen at 2000 if in traffic......usually backfire through carb is lean ..like before drilling out and adjusting air mix screws ... would backfire through carbs all the time when stock and fully warm... opened up air mix screws 90 % went away...ill get a pop through carbs once in a while and only when grabbing throttle to downshift..think thats normal for a stock set up....can open air mix more but why do that and have it run rich....your popping through carbs sound like different problem