Over the weekend boat ran great all day on the water. Started it to bring it back to the launch and it wouldn’t run past 1800 rpm. If it happened to feather over 2k it would run great again up to 5500 rpm. Tested compression all are 115-120, getting good spark , all fuel system has been replaced and carbs are all getting fuel. Tested stator and low side seemed to be out so while I was there replaced the stator, trigger, both switch boxes, new plug wires. Timing is correct, flywheel magnets looked good, but now I start the boat and it hardly wants to idle and backfires through the exhaust…. I’ve gone back through all the wiring , cleaned grounds, checked mixture screws on carbs and I cannot figure it out. I’ve tried advancing timing to see if the backfire goes away but it still persists. No water in fuel, checked with an external tank. Any help would be greatly appreciated!