Hello everyone. I am new to the forum and new to motorcycles. I have an '87 VN750 that has had a lot of carb work done on it (no mods, all stock). Once I got it running, I installed a set of cruzers. Now, I have a popping and backfire between 3 and 4k rpms when downshifting or letting off the throttle. Attempted to adjust air/fuel mixture screws. Rear carb was turned out about 4 1/4 turns and rpms still increasing. Bike never bogged down or shut off with both screws all the way in. No ear shave and don't plan on it Here's the question. Do I need to just keep tinkering with air/fuel mixture screws, rejet, or just live it. If rejet is required, whick kit should I get? I know nothing about the jet sizes. Thanks!