Geir,
I have stock pipes that are almost "gutted". 130 mains and stock pilots. I could not get the popping to stop. I checked my float bowl level and found my left carb level was 7mm low and the right one was 6mm high (rich and occasionally flooded). I got my float bowl levels set right, then adjusted the idle mix screws the old fashion way. (by removing one spark plug and starting the bike on one cylinder - adusting the screw out until it it sputtered and screwed it in until maximum idle was acheived. Then I split the difference on the screw setting. Then the same with the other cylinder.) After I did that, I balanced the carbs with a mercury manometer. My acceleration and deceleration are as smooth as silk with no pop or backfire.
OK, my left screw is turned out 4 turns. My right screw is turned out almost 3 turns. Why so much difference?
That darned right carb fuel level is high again! 
I may get someone to help me in Georgia this week.
