Why would a (carb'd) bike backfire on starting?

[monkey]

Just curious. My ZX6R today done a cracking backfire the second the starter was pressed today. It's never done anything of the sort and hasn't been ridden since Friday.

Explain.

Thanks!

[yorkie_chris]

Bit of fuel in the pipe, nowt to worry about.

[plowsie]

Your sig explains it...

[philbut]

Bit of fuel in the pipe, nowt to worry about.

+1. my SV did it in the middel of Leeds uni campus after a conference :smt082:smt082:smt082 oh how the students jumped!

[yorkie_chris]

I park in front of MechEng building with pipe facing towards bus stop. Usually 40 or so people at it at 5pm. Watch them cower! Muahaha

[custard]

my hornet used to do it.

great fun, except the time when immediatly after it had gone off, the police sirens came on...

[Sid Squid]

This was written in answer to another related question, and I don't know if your bike was cold or hot or if you'd used the choke or... other things but the principle remains true:

If you fire up your bike from cold in marginal conditions, it's not unusual to get either a partial, or sometimes a complete misfire, the resulting unburnt fuel rich gas gets shoved into the pipe on the exhaust stroke, next charge goes into the cylinder, fires, and then extremely hot gas gets let into the pipe where aforesaid eminently burnable gas lies waiting to p*ss your neighbours off, voila , big bang in the pipe, enjoy.

Possible causes:

Plugs need a clean/change.
Battery voltage low: Poor quality and duration sparks.
Old or contaminated fuel.
Incorrect choke setting.
It's bloody cold out.

[monkey]

Ah that'll probably be the incorrect choke setting then.

Thanks!

[johnnyrod]

My old GSX250 did that when it was wet, just a misfire. Awesomely loud sometimes.