Ok here is my problem , i just got my bike back from the shop today 2007 883 ,,,i had the 1200 conversion done ,,,,bike runs great very strong ,,,but when i let off the throttle it pops like backfiring alot ? guy at the shop said it needs new pipes that doesn't have the cross over tube on the bottom like mine ,,,but i just put those pipes on there a few months ago with all new gaskets...didn't do that until they worked on it ,,,any help would be great