On Tue, 17 Mar 2015 05:11:47 -0700 (PDT), TimR
wrote:

When I was growing up car backfires were common. As a kid I had friends who could make it happen at will.

Now that the carburetor is long gone, most younger folk have never heard one. Fuel injection eliminated this, I think; could be wrong.

I never understood exactly what happens. Usually a car would backfire when under heavy load, and the gas suddenly let up. So my guess is the carburetor had a full charge with nowhere to go. But what ignited it?

Or, possibly the lack of air made an overly rich mixture escape the exhaust valves, and the explosion was in the manifold?

Timing caused it. If the distributor was installed off by a tooth or
three. Timing could also slip if the nut loosened a tad.

Carbs caused it. Adjust dual four barrel carbs or three-deuces. Have
to get the cabs in tune. Flooded and it would catch fire so have a
shop rag handy to toss of the carb.

You could push in the clutch in, turn off the ignition, release the
clutch, turn on the ignition and cause a back fire. I was told it
could pop off the top of a piston but I never saw or heard of it
happening