What causes a backfire?

[Mattastic]

It's only ever happened to me once but I do not know what caused it. I was going down a slight hill with the throttle open about half way (6 to 7 thousand revs) and noticed the lights were on red so I shut the throttle off and put my brakes on. Almost as soon as I had shut off the throttle there was a mini "explosion" from my exhaust! It's never happened before or since but got me wondering what could have caused it.
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Too skint to buy a bike

[craigT19]

a back fire happens when exhaust gases build up in your exhaust, when u shut the throttle off, you were reducing the amount of fuel being fed in...but there was likely an excess amount of fuel already in there because you had the throttle open, so when this fuel ignited the exhaust valve may have been slightly open causing it to ignite the exhaust gases causing a backfire
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Bikes owned :- 2001 nsr125, 1999 zx6r, 2006 yzf-r1, 2009 xmax 250, 2012 yzf-r1, 2015 MT-07
Current bike : - 2016 MT-10
BCF member pops. sadly missed 1945-2003

[Ninja]

or simply - unburnt mixture passing into your exhaust on the overrun being ignited in there by the next hot discharge on its way out from the pot
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James
4 wheels transport the Body ... 2 wheels transport the SOUL

[dandit]

[bikedudextrm]

I was told by someone that if you keep back firing (like i do) it can eventually damage the main bearings. Something to do with when you do it theres more fuel being combusted so it causes more stress on the top/bottom end.

Didn't quite know how to describe it, but is it true.

[Ninja]

No - only the exhaust seals/ joins/ baffles may be affected by repeated pops and bangs
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James
4 wheels transport the Body ... 2 wheels transport the SOUL

[dandit]

[Laura]

I thought backfires are caused by the system sucking in cold air?
Poppy does is fairly regular.
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Good girls ride motorcycles bad girls thrash them.

[kev]

If you keep making your bike backfire it will damage your valves and kill the baffles in your exhaust.
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20:02:36 Jammy-R6: any holes a goal
20:02:48 kev: even if its a hairy mans arse
20:02:56 Jammy-R6: hell yes

[mr.z]

Can you cause a back fire by hiting the kill swich then switching back on then? will the engine keep going if you hit it "accidentaly" then put it back?
allthough i gather from what kev put its not a great idea
An instructor of mine said "watch this" when passing some school kids, >BANG< bit nawty yes but very funny

In what way will it damage the valves? bending them?
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>RidingSkills<->Tech Tips<->MyBikes<

[Shaun]

[Demonic69]

Hmm, best stop the bangs then hadn't I
And I thought they were caused when you hit the kill switch at over 6krpm
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Back on a Blade. Just feels so right.

[zaknafien]

I remember riding to stew and M's with us backfiring all the way.
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02 Firestorm.