Why does a motorcycle backfire when you let off the gas?

Answer by  qos (226)

If your motorcycle isn't set up properly or is cold, then some unburnt gas will end up in the exhaust pipe. This unburnt gas is then ignited by the heat of the exhaust, causing a small explosion and the noise we call a back fire.

Answer by  kate74 (273)

When you twist the throttle, gas is put into combustion chamber but if it doesn't get all the way there (because you let off the throttle, reducing push into the chamber), it'll just catch a spark. The spark has to go somwhere, so it exits the exhaust, causing the bike to backfire.

Answer by  Amber40 (24961)

This is usually a sign that your bike is running rich. Excess fuel is being pulled out of the cylinders and is hitting the hot exhaust. This cause it to light off causing a pop. You should check your plugs and make sure that you are not running to rich. If you are then you need to tune your carb.

Answer by  Amber40 (24961)

This could be caused by a few different things. One possibility is that your timing is off and the bike is firing while the exhaust valve is open. More than likely thought your bike is running too rich. There is too much fuel being delivered to the cylinder and not all of it is burning. Check your plugs and timing.