BACK FIRING

Hawke's Bay Tribune, Volume XXIII, Issue 72, 7 March 1933, Page 10

BACK FIRING

NO NEED FOR ALARM. Alarm is sometimes experienced by those who are driving their first car, :o find that when taking their foot off he accelerator pedal, while driving ilong a level road, and especially downlill, to hear a series of loud explosions )ccur in the muffler, known as backiring; and there are probably very few ■ar owners who really know the cause, ind may imagine that their engine is jadly out of tune. Backfiring in the nuffler is likely to occur on any car ivhen the toot is suddenly removed rom the accelerator pedal or when .ousting, so that the car is “pushing’’ :hc engine. Theoretically, what happens is this: fhe sudden closing of the throttle remits in a very high vacuum in the ntake manifold. This excess vacuum nterferes with the incoming charge, producing an over-rich mixture which s not completely burned, and is consequently pumped into the exhaust nanifold and muffler along with the whaust gases. 'I he heat in the muffler .hen vaporises this over-rich accumuation, and when it reaches the proper Rate, it is exploded by other charges Tom the exhaust manifold. This proluces the backfiring noises in the nuffler. If these explosions occur too frequently, it might be well, of course, -o have the carburettor inspected, as ?ases have been known where the needle valve is worn and an over-rich ■nixture has resulted, leading to imperfect carburation.