engine back fires


Old 07-20-03, 09:43 AM
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tractor back fire

I have a 14.5 mtd lawn tractor that started to back fire when I turn the engine off. Any idea's as to why and if it will harm anything. Thanks
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Old 07-20-03, 11:02 AM
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Question More Detailed Info Requested

Hello: ThomasB

Backfiring is distructive to the exhaust system as well as the engine and internal parts. One possible cause is a lean fuel mixture. Which can indicate a restricted lean fuel circuit in the carb or a carb low speed screw set to far inwards.

Most likely the forum professionals have several other possible causes. Valves are one and timing may be another. More specific detailed information would be greatly appreciated.

Kindly post the engine brand name, model, year & serial numbers. These numbers help to identify the specific engine model and the parts used to build it.

Doing so would greatly improve our chances of offering you specific corrective advice, helpful suggestions, technical problem diagnosis assistance, professional repair methods, procedures and technics plus the possible parts causing the problem your describing.

To add more detail use the REPLY button. Using the reply button moves the topic back up to the top of the daily topic list automatically & keeps all communications in this one thread.

Lawn mower shops and or small engine repair shops can also help determine what the possible problem may be. Bring the year, make, model and serial numbers and stop in at the store. Parts and repair manuals are also available at these stores. Locations can be found in the local phone book directory.

Regards and Good Luck, Small Engine Forum Moderator
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Old 07-20-03, 10:26 PM
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Backfiring is very destructive as mentioned. It is a sudden explosive force to the internals of the engine. It could cause the top compression ring in the engine to break which would lead to possible cylinder scoring and also fackfiring could damage the spark plug. One cause of backfiring when shutting down is not letting the engine idle down long enough before shutting down. Another cause is that maybe a piece of carbon is stuck to the valve which could get red hot and when you shut the engine off it would ignite the incoming fuel. When an engine back fires, it is doing so while the exhaust valve is open hence the reason a hot piece of carbon could ignite the fuel mixture at the wrong time. The fuel mixture could even get blown out the cylinder and into the hot exhaust where it could also ignite. I have seen a hole get blown open on the side of the muffler just from a sudden backfire.

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