Muffler

What do you mean by a blown muffler? I take it you didnt notice any backfires that might have caused a muffler failure?

AlvaG wrote: Well, the first time my wife says she did here a backfire. It blew the end and the top out. This time my kids did not notice a backfire - just the loud boom from the top being blown out of the muffler. After reading some things here, it sounds like it could possibly be repaired. I just want to try to fix whatever is causing it. Thanks

The boom that your kids noticed is more than likely the same thing your wife experienced. Replacing mufflers twice a month is going to get very expensive. I would replace them with straight exhaust hose until I nailed down the problem. Is your boat carbureted or fuel injected?

Alva, before the backfire, did you have an exhaust leak on one of your manifolds? A backfire in the exhaust is usually caused when the butterfly valve in the carb suddenly closes. What happens is,.... after the valve is closed but before the RPMs are reduced to idle, excess fuel (more than the cylinders can burn) is being drawn into the engine. When this excess fuel reaches the hot exhaust most of the time nothing happens,.... it goes straight through because there is not enough oxygen in the exhaust to burn it. But,.... if you have an exhaust leak the story changes. Hope this helps. Brian

Alva, I ask about the exhaust leak because that is a source of air (oxygen) to be let in to the exhaust system. A temporary vacuum can be created in the exhaust (in the area of the manifolds) when the throttle suddenly closes. This can draw air into the exhaust system and create a combustible mixture. Of course fuel would be required too. This would be met by the scenario I stated above.

Other things that can cause backfire are late ignition timing and/or bad (or crossed) spark plug wires.