Massive bang at start-up

[maz66]

Sometimes when i start my ZXR, a very loud bang, like a gunshot fires out when its just about to turn over. I actually think someone has shot for an instant. IT's also becoming more frequent, say every 2 weeks - not what i need early in the morning!. It hasnt had its oil change since christmas and needs a full service soon although i don't do many miles, could this be the reason? cheers

[superman]

na you will find that its the petrol firing up, there is a tiny amount coming through when you shut the bike down, mine used to do it if i didnt start it for 2 days, best way to stop it happening is to turn the fuel to off before you put it to bed for the night, but dont forget to turn it back on in the morning lol, put a note near your bike to remind you,... hope that sorts it for you.

[masterofinsanity]

unburnt fuel, bike could be running rich or as you say in need of a good service.

[maz66]

unburnt fuel, bike could be running rich or as you say in need of a good service.

I think it could be all 3, thanks guys!

[liam7200]

i think it's what superman said my crosser used to do this all the time cause i never shut off the fuel,it just un-burnt fuel exploding when u strt it.
It should'nt cause any damage, give it a service and iv that does'nt stop it you could always try turning the fuel off!
its also use to happen when ever i left the choke on!! ive none of above work you could try:

having a look at the carb to see if its stuck open?
even a mm can cause fuel to leak in?

[stug]

I heard of bikes years ago going on fire after back firing if it was bad enough it back fired through the carbs setting the filter alight.
Probably only do it on bikes with the airbox removed and sock filters though.