What causes a 66cc two cycle engine to backfire?

C1500 or K1500?
pickup right,?
what engine is there of 6.
the VIN answers all that but not told
called backfiring to throttle body,
causes are: (Gas engine otto cycle)
1: valves burned or stuck open. (compression test?)
2: valve (in head) timed wrong.
Spark timed wrong or wrong firing order.

• There could be several potential reasons why your 1996 Silverado with the 5.0 Vortec engine is not starting and is experiencing backfiring when you try to start it. Some possible causes of these symptoms include:A faulty ignition control module (ICM): If the ICM is not functioning properly, it can prevent the engine from starting and cause backfiring when you try to start it. You may need to replace the ICM to fix this problem.A problem with the fuel delivery system: If the fuel pump, fuel injectors, or fuel pressure regulator are not working properly, it can prevent the engine from starting and cause backfiring when you try to start it. You may need to diagnose and repair any issues with the fuel delivery system to fix this problem.A faulty engine control module (ECM): If the ECM is not functioning properly, it can prevent the engine from starting and cause backfiring when you try to start it. You may need to replace the ECM to fix this problem.A problem with the ignition system: If the spark plugs, spark plug wires, or ignition coil are not working properly, it can prevent the engine from starting and cause backfiring when you try to start it. You may need to diagnose and repair any issues with the ignition system to fix this problem.To diagnose the specific cause of the starting and backfiring issues on your 1996 Silverado, you may need to perform further testing on the ignition and fuel systems. This will help you identify the specific problem and take the appropriate steps to fix it.

There are many reasons that a vehicle will backfire through the carburetor. What determines the cause depends on what condition the backfire happens. Is it a steady backfire at idle or does it start when you are accelerating ? Do you live in a wet climate or dry? Has the engine been wet?
Backfiring is caused when the exhaust valve is open during the firing or compression stroke of a certain cylinder. For example, a broken spring will not close the valve completely. A bad camshaft lobe will cause a back fire, if you have a distributor that got wet the spark could cross over to another area wire and cause the problem causing a missfire. If the wires were put on wrong after putting in plugs it will cause a missfire.

Check this video for idle speed adjustment. Backfiring can be caused by incorrect mixing in the carburettor or bad timing settings.


Check this link for backfire issues:

. What would cause Ford 390 to backfire through carb Yahoo Answers

Setting Curb Idle Speed of Carburetor Video Holley Carb DVD

The distributors on these GM trucks should be replaced at least once a year. Any check engine light on? The crank sensor can cause it to backfire as well.

Most of the time an engine that backfires is out of time. I would
check this first, as this is the problem 95% of the time. It could
also be bad fuel, a bad catalytic converter (rare) A bad coil or igniton module will definatly cause it. A fuel injector that is spraying excessive
fuel out will cause an engine to backfire. Burned or leaking
valves will cause it (rare).

http://www.ehow.com/list_6402725_causes-engine-carburetor-backfire.html

There are two kinds of backfires, one is produced from the engine air intake and the other is produced from the tail pipe of the exhaust system. The cause for a backfire condition can vary depending on the malfunction of a particular system. Some backfires can be extreme enough to cause damage to related components. Anytime a backfire is observed immediately diagnose and repair as needed. If the engine is running rough it can produce a backfire. A backfire occurs when there is an imbalance in the air to fuel ratio required for your vehicle to operate properly. If the fuel mixture is too lean (not enough fuel) you may have a backfire in the intake manifold gasket, or too rich (too much fuel) you may get a backfire out of the exhaust system. It is important to observe the location of the backfire.

Sounds like an ignition or timing problem.
Is the check engine light on ?
This engine uses a direct ignition system which means each cylinder has a coil on top of the spark plug. It could be as simple as worn out spark plugs.
If you had said the engine backfired and was hard to start, but no flooding, I would also look at low fuel pressure. But too much fuel causes flooding.
A faulty throttle position sensor could cause all of your symptoms, but it should set a trouble code and turn on the check engine light.

Backfires are usually caused by a lack of fuel...change the fuel filter. Also very old spark plugs (or plugs gapped to wide ) will cause this problem.