Car backfires through the carburetor are sometimes caused by a lean air/fuel mixture. Backfires may also be caused by a leaking hose, faulty plugs or the brand of fuel being pumped in.
Backfiring is a loud bang or explosive sound that occurs while the engine is idling down or shortly after the engine has been shut off. Most backfires through the carburetor arise as a result of faults within the ignition system. Fixing these faults is often enough to solve the problem.
Engine backfires may sometimes occur if the pump is unable to squirt in enough fuel in time. This may be because the pump is plugged up or simply not working. Changing the pump fixes the problem.
A faulty ignition system is a possible cause of a engine backfire. For engines to run efficiently, the spark plugs have to ignite the air and fuel at the right time. Incorrect timing can lead to the fuel being ignited before the manifold intake valve closes, causing a backfire through the carburetor or exhaust.
Holes in the pipe leading to intake manifold may result in an increase inflow of air, which unbalances the air-fuel mixture ratio. A leaner ratio is more volatile, and more likely to cause backfires.