Best way to sync carbs is using mercury sticks or vacuum gages, BUT another way that gets them close is to get a piece of rubber tubing, approx 1/8" id. x 18" long remove air filters and put the tube into the venturi approx. 1" and listen to the pitch through the tube. Make sure you put the tube in the venturi's the same amount. Its an old timers trick and is better than nothing. I don't have carbs mines EFI.