Re: Backfire

Posted by H.L. Chauvin on April 12, 1998 at 18:26:53

In Reply to: Backfire
posted by Jack Cunningham on April 11, 1998 at 10:17:45

: I'm a new owner and know very little about the "A" but I'm learning. What am I doing wrong when after stopping the car and turning the ignition off I get a beautiful explosion from the muffler! I stopped for gas yesterday and had everyone diving for cover.
Hi Jack, Some other causes for explosion from the muffler are e.g., a sticking valve, (engine not run for several months), or weak valve spring, or bad valve seat, or piece of carbon on valve seat area, causing a gas/air mixture leak.It appears that the gas/air mixture could be exiting the combustion chamber through an ill timed valve or opened valve and may be ignited by a burning ember of carbon residue as opposed to the ignition system, which is off.Maybe first try checking valve seating with a compression test of the four cylinders.If this is okay, try disconnecting the muffler and running the engine at night, in a dark place, to check the gas/air mixture by observing the color of the exhaust, above idle speed:Red = too rich, too much gasoline;Yellow = too much air, (could be mainfold leak, vacuum hose intake leak, carburator gasket or carb./manifold gasket leak); Blue = okay, (looks like a gas water heater flame, or gas range flame).Even though messy, while engine is running, manifold leaks can be detected by applying lubricating oil to joint at manifold gasket to see if oil is drawn in at leaks. Does explosion occur with muffler disconnected?
Let us know what you find!Best wishes, Henry.

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