Can an old timer explain car backfires?

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On 3/18/2015 12:16 PM, Stormin Mormon wrote:

(from another friend)
The original purpose of the Vibrator was in the power supply of early car radios. The Vibrator would make pulsed DC to drive the transformer to make the B+ (Typically 300 Volts) and C voltage (Typically around 45 Volts) to run the old High Voltage tubes.
When I was Young and Dumb, I had a 1972 Impala 454 SS with dual exhaust. I made me a Vibrator powering a pair of Ignition Coils driving a pair of Spark Plugs I mounted in the exhaust tips. When I flipped the switch, it would throw flames about 3 or 4 Feet long out of the back.
This trick works best on Pre-1974 EPA cars then the newer ones.
.
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Well, as a mechanic I can say definitely it could NOT damage a piston - as the "explosion" was not in the engine. Bad ignition was responsible for more exhaust bachfires than bad carburetion. My Dad's '69 GMC pickup had a bad habit of slitting the muffler every 6-8000 miles unless you changed the points first. Ends up the factory had not installed the ground wire between the points plate and the distributor housing, so the points burned badly - and intermittent spark would allow the muffler to load up with gas when the spark was off, and then light when it came back on.
An exhaust leak could also cause exhaustr backfire on decel or over-run as the exhaust was rich with gas from the high vacuum, and added air into a hot pipe would light it off, giving bang-bang-bang-BANG!!! coming down a hill.
One day with 22 tons of farm equipment on the float behind the 292 GMC, I came down a long gentle hill to a narrow bridge across a creek where guys were working on the road.. They were in no hurry to get out of the way as I came towards them, so I shut off the ignition for a second or two, then turned it back on. They jumped out of the way real quick!!!. (had a drawn steel "cherry bomb" muffler on it that withstood backfires quite well - after blowing a few Thrush cans off of it.
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I think muffler backfire can be from too rich. Carb or intake backfire, too lean. I had backfire in a datsun. I had to readjust airflow meter.
Greg
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