A carburetor backfire describes the small explosion that sometimes occurs when starting up a car. It generally makes a loud sound, like a gunshot, and occasionally is accompanied by a visible flame.
What Causes a Backfire
Generally, a backfire is caused by an imbalance in the air to fuel ratio. Either the engine is not getting enough fuel, which is also called running lean, or the engine is getting too much fuel, which is also called running rich. There are a few different issues that can create this situation.
If your engine is not timed correctly, it may backfire. If your car has an ignition distributor, adjusting it may be able to correct a timing issue. Otherwise, the timing of the engine will need to be adjusted with a timing light.