Exhaust line? Not sure what you're talking about. When you pump the primer bulb, does water leak out of the front of the carburetor? If so, you have a needle/seat problem in the carb. Check your plugs to see if one is saturated with fuel after running, if so, you have an ignition problem and that cylinder isn't firing and burning the gas. A year and model number will get you a lot more help and information.
