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:''For other meanings of the term, see backfire (disambiguation).'' A back-fire or backfire is combustion or an explosion produced by a running internal combustion engine that occurs in the air intake or exhaust system rather than inside the combustion chamber. Unburned fuel or hydrocarbons that are ignited in the exhaust system can produce loud sounds even if flames are not present at the tailpipe. A visible flame may momentarily shoot out of the exhaust pipe where the exhaust system is shortened. Fire may also travel into the air intake piping. Either condition may cause a loud popping noise, together with possible loss of power and forward motion. A back-fire is a separate phenomenon from the fire produced by Top Fuel dragsters. Also, an explosion in the inlet manifold, carburetor/throttle body, or air cleaner of an internal combustion engine can occur when the intake valves are not shut prior to fuel combustion. The term derives from parallel experiences with early unreliable firearms or ammunition, in which the explosive force was directed out at the breech instead of the muzzle. From this came the use of the word "backfire" as a verb to indicate something that produces an unintended, unexpected, and undesired result. == Explanation == Backfiring in internal combustion engines occurs outside of the combustion chamber, and is typically the result of an improper air to fuel ratio. An overly lean air-fuel mixture (i.e. an overabundance of air) can lead to a failure to ignite in the combustion chamber, also called a "misfire". The unburnt fuel then enters the exhaust system, where hot components can cause the fuel to ignite unpredictably. Alternatively, rich air-fuel mixtures (i.e. an overabundance of fuel) can result in incomplete combustion, again causing unburnt fuel to enter the exhaust system. Backfires may also occur before the combustion chamber. One possible cause of this is timing. If the timing is too advanced, the spark plug fires before the intake valves close, causing the combustion to propagate into the intake manifold, further igniting the air-fuel mixture there; the resulting explosion then travels out of the carburetor and air filter. On many small marine engines, a screen is placed over the intake of the carburetor as a flame arrestor, to prevent these flames from escaping the intake and potentially igniting fuel or fuel vapors in the enclosed sump or bilge of the boat, causing a fire or explosion. Alternatively, the ignition timing may be retarded, in which case the combustion is not completed by the time the exhaust valves open, allowing the combustion to propagate into the exhaust system. Additionally, improperly adjusted carburetors that create a lean condition during acceleration can cause the air fuel mixture to burn so slowly, that combustion is still taking place during the exhaust stroke, and even when the intake valve opens. The flame front can then travel up the intake and cause a backfire. In this situation it is conceivable that there is a backfire occurring in the intake manifold and exhaust manifold simultaneously. In both cases (combustion occurring ''before'' and ''after'' the combustion chamber), the result is a sharp pop, which is colloquially referred to as a "backfire". However, for troubleshooting, engine mechanics more strictly define an ignition of fuel within the engine ''exhaust'' system as an "afterfire", while a "backfire" is this same process taking place in the ''induction'' system. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Back-fire」の詳細全文を読む スポンサード リンク
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