What makes a motorcycle backfire?

A too lean (too much air and not enough fuel) mixture will also cause a backfire. Lean mixes burn slowly and as a result you have combustion occuring in the exhaust ports and pipes. Since this occurs when you have the throttle closed, you need to richen up the idle mix.

If your bike has carbs, you need to get to the idle mixture screws. Some regulate air while others regulate fuel, so you need to consult a manual of mechanic familiar with your particular model.

If fuel injected, the fix isn't as easy and you need to talk to someone who knows how to tinker on your bike's injection system. Without going to a power commander type fix, you need to fool the computer into thinking the engine is running colder than it really is so it will inject more fuel.

Since you say running with the choke on helps, I assume you have carbs. The "choke" lever on fuel injected bikes is actually a fast idle lever, nothing more. Running with the choke on won't hurt a thing as long as you aren't running so rich that the engine misses, blubbers and smokes black out the exhaust. If it stops the backfiring, then it's actually better because that way you're not putting a burning combustion mixture through the exhaust valve. A still burning mix greatly increases the temp and can burn the valve and seats.

Motorcycle Backfiring

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RE:

What makes a motorcycle backfire?

I own an '06 Suzuki S40. I have noticed that when I am going down a heal and therefore am not riding the throttle the bike tends to backfire. First off what causes this? Secondly is this bad for the engine or exhaust system?

I have noticed that I can adjust the choke to avoid this however the bike...

You didn't say whether it backfires on acceleration or decelaration. If it backfires on acceleration, the mixture is too lean. That means that you got to keep a little bit of choke on untill you've ridden it for a couple of miles or so. If it backfires on decelaration, it could be you have an air leak into your exhaust system, when that happens, the exhaust sucks in enough air to make the unburned exhaust gases combustible and that's when the backfire happens.

Backfire Moto

Running with the choke on is constantly running rich. When you back down, some gas is passed to the exhaust system, the heated gas is the backfire you hear.

If you need to constantly run with the choke on, you likely need the engine checked out by a good shop, getting it right should allow you to run without the choke, and stop the backfire.

Have the carb set up by a good shop. It is most likely running lean. Running with the choke on is better for the motor than running lean.

How was the problem fixed ? I have the same problem and the workshop cant seem to fix it. That said they have not looked at the carbs in detail. Just cleaned them

i have a honda aviator white colour when i accelerate there is no back firing buh wen i deaccelerate n wen it cums down to 20 speed it starts back firing hows it ??

i have the same problem with 06 1400 need help