I've been getting really loud backfire. I've been trying to figure out why but with very little knowledge I can't get far. Sometimes it happens after I turn the bike off and sometimes it happens when I've given the bike throttle. Maybe that'll help with diagnosis but not really sure..help is really appreciated

when you shut the engine off, are you in neutral or have the clutch disengaged?  I've had backfiring happen when  my engine shuts off but the clutch is still engaged.  This is because gas is still being pulled through the engine by the rotation of the tires, and it makes it to the hot exhaust system which ignites it.

All this being said, I'm relatively new to riding so anybody else care to confirm?

Edit: backfiring at speed is usually a result of fuel starvation, which I think happens to me on my '00 gs500e on the freeway sometimes.

When you say backfire, is it true backfire (fire comes back through the carbs), or is it out the exhaust (afterfire)?

Do you have any modifications in terms of jets, filters, or exhaust?

Quote from: RossLH on September 08, 2013, 02:01:39 PM
When you say backfire, is it true backfire (fire comes back through the carbs), or is it out the exhaust (afterfire)?

Through the exhaust backfire

I only have a Uni foam air filter that's my only mod

It could possibly be running lean. Did you check the spark plugs? They'll usually tell the story if it's been going on for a while.

If this problem has only surfaced since u put the Uni foam filter on perhaps it's time to go back to stock....if u want a quick fix.

this problem occurred to me when i had a bad battery. after changing the battery up to something good, the shorai battery, the problem went away.

Remember that our plugs fire on compression AND on exhaust. We have that extra wasted firing.
If your battery was bad, probably the main firing was weak. Then during exhaust when the plug fires again, it ignited the unburnt stuff as it was expelling it out the exhaust.

Our ignition fires every rotation of the crank. It doesn't know we are a 4 stroke engine and really only need to fire every other stroke.

It would be cool to modify the ignition to fire only when needed.

Backfiring out the exhaust can be simply unburnt stuff igniting with the extra spark at that time.

Does that count for Jardine systems, too? I chalked mine up to being a function of a performance exhaust.

Quote from: adidasguy on September 09, 2013, 04:54:56 PMBackfiring out the exhaust can be simply unburnt stuff igniting with the extra spark at that time.

It doesn't even need a spark, really. If there's unburnt fuel, most (if not all) of the oxygen has been burnt off, and the spark will not cause ignition. That unburnt fuel gets superheated in the exhaust gases and autoignites as soon as it comes into contact with oxygen.

Unless, of course, you have a PAIR system intact. That'll introduce extra oxygen into the exhaust and burn it off earlier.

Quote from: RossLH on September 09, 2013, 05:54:18 PMUnless, of course, you have a PAIR system intact. That'll introduce extra oxygen into the exhaust and burn it off earlier.

My GSX650F started making a racket on compression after I added a Yoshimura slip on, I plugged the PAIR and the noise went away. The consensus was...that it was always happening even with the stock pipe, you just heard it more with the Yoshi 

EDIT: A leaking exhaust gasket at the head is a good way to introduce some oxygen to mix with the fuel in the pipe 

Check your diaphragms in the carbs. I had one develop a small hole and it introduced all sorts of backfire out the pipe. Like shooting flames out the pipe style backfire