ABOUT BACKFIRING.

King Country Chronicle, Volume XXVI, Issue 3440, 8 March 1932, Page 2

ABOUT BACKFIRING.

Alarm is sometimes experienced by those who are driving their first car, to find that when taking their foot off the accelerator pedal, while driving along a level road, and especially .downhill, to hear a series of loud explosions occur in the muffler, known as backfiring; and there are-probably very few car owners who really know the cause, and may imagine that their engine is badly out of tune. Backfiring- in the muffler is likely to occur on any car when the foot is suddenly removed from the accelerator pedal or when coasting, so that the car is "pushing" the engine. Theoretically, what happens is this: The sudden closing of the throttle results in a very high vacuum in the intake manifold. This excess vacuum interferes with the incoming charge, producing an over-rich mixture which is not completely burned, and is consequently pumped into the exhaust manifold and muffler along with the exhaust gases. The heat in the muffler then vaporises this over-rich accumulation and when it reaches the proper state, it is exploded by other charges from the exhaust manifold. This produces the backfiring noises in the muffler. If these explosions occur too frequently, it might be well, of course, to have the carburettor inspected, as cases have been known where the needle valve is worn and an over-inch mixture has resulted, leading to imperfect carburation.