I have a 2003 Honda Foreman 450ES and when you are going down a hill and slowing down by downshifting or decelerating there is a loud backfire that sounds like a shot gun going off. The quad has been buried in a lake before could this be caused by a plugged exhaust? The carb has been cleaned and gaskets replaced with a stock jet set up. A new OEM exhaust is fairly pricy and a new aftermarket exhaust is about $400 so I don’t want to replace it if i don’t have to.