Loud *bang* at startup?

[Teh_K]

My gf and I were getting ready to go ride, and when she started her '99 600 there was a loud(!) BANG 1st thing when the engine turned over. And then it ran fine after that.

Was that a backfire? Is it a really big issue?

[md86]

Yup , and maybe .

[duff daddy]

yea it was a back fire, you could have shut off the bike and had the rev's a lil high last time you rode it so the motor was off but it was still pumping a lil gas in to the motor and exhaust had un burnt gas, now when you go to start it that left over gas combusts and theres your bang

[The CyberPoet]

Check to make sure the bike's fuel petcock setting isn't on PRIME. Sometimes kids and nitwits come along and change the setting. If it is on prime, you may have a sticking float bowl issue that you hadn't noticed before...

Normally a bang on start-up occurs because there is more fuel in the cylinder than wants to ignite completely; it gets out into the exhaust (where there is extra air to mix with), and then gets ignited by the hot exhaust coming out of a different cylinder. Usually it's an once-in-a-blue-moon thing.

KNOW THIS:
don't rev the engine just before shut-down (increases the odds of this occuring, and of other secondary issues). Let it idle for a few seconds and then kill it.

Cheers
=-= The CyberPoet

[Teh_K]

Ok, here's a little update:

Her idle was indeed way too high. It would idle normally when the bike was cold, but upon returning home (when the bike was obviously warm) her idle was at, like, 3k. So, I turn the idle screw and get it down to ~1.2k while the bike is still running/warm and turn it off.

The next time we went out riding it backfired again, even though I adjusted the idle...

I'm hoping it will just go away by itself now that the idle is fixed, but what are some other possibilities?

[Mojoe]

there aren't really any other possibilities. if it was common that you had to turn the engine over for long periods of time and had alot of backfiring, then you could have ignition or fuel problems....but with it just being this one incident, do not worry about it.
having 3k idle was probably the culprit. extra gas was probably being drawn in after you killed the ignition cuz of the higher rpm. it should be fine now that you turned it down.

[donmega]

take off the airbox and turn the petcock to prime and I bet you have a carb leaking fuel


With it being a 99 try to clean the carb float bowl before buying rebuild kits.

[Teh_K]

For some reason carbs scare me, so I hope that's not it

However, it hasn't backfired anymore since my post above so I think we'll wait until (or if) it happens again.