What causes backfire?

Question

When letting off of the gas, what causes "backfire" - which I believe is occuring in the exhaust/muffler? To rich, to lean...???

Answer 1

change you spark plugs and decarbonize your engine

Answer 2

Well timing, burnt valves, but most of the time timing is the reason. If it is to retarded on timing it will back fire.  

Answer 3

I think backfire is caused by preignition in the combustion chamber. The momemtum of the vehicle is moving the pistons and since they are dragging, the entry of the fuel/air into the combustion chamber pre-ignites when the rotation of the crankshaft is deaccelerating.

This is much more preferable to acceleration with preignition which causes knocking, which really sucks.

Backfire isn't typical in fuel injected engines. It's typical in carborated engines.

Answer 4

timing

Answer 5

too rich. the gas is,nt all burning up.

Answer 6

Any mixture condition, lean or rich, that interferes with proper combustion can cause "backfiring" - actually, it causes "afterburning", where the unburned mixture gets ignited when it is exhausted into the hot manifold.

True "backfiring" comes up through the intake, and is related to really bad timing, cross-firing in the distributor or from bad plug wires, or from sticking intake valves.    

Answer 7

Bean burritos

Answer 8

Back firing is caused by unburned fuel being ignited in the exhaust system, usually the muffler or catalytic converter.  This can be caused by several things. Ignition timing, rich fuel mixture, or valve timing etc.You need to take it to a professional.  You can not check it out without the proper equipment.  

Answer 9

Usually it is engine timing. It could be bad fuel also. I have seen Catalytic converters cause the same symptom. A bad coil could cause it by jumping posts. Excessive fuel out of a injector can cause that too. You need to take it to a shop to figure this one out. I hope this helps.

Answer 10

If the fuel mixture is too rich you'll get unburnt fuel building up in the muffler. The easy way to tell that is when you accelerate you'll see a dark black smoke coming out of the exhaust.

Dark black smoke is unburnt fuel and light grey bluish smoke is oil

Once you get unburnt fuel building up the muffler a bit of heat or flame down the exhaust will cause it to ignite causing backfiring.