Backfire

[mark553]

Hi does anyone have any ideas what is causing backfire on bike please

 

[rebeltaz83]

Air leak. Let it idle and spray around the carbs. And joints with carb. Cleaner, when the idle smooths out, you found your leak. I'd say starting fluid, but unless you have fire insurance I'd use carb. Cleaner, or brake clean.

 

[sdt354]

Time for a shotgun cleaning? Assuming it's a Gen 1. Lots of good threads on it here.

 

[dannymax]

If it backfires on decel it could be a bad air cut off valve

 

[racerboy]

Its never ending. Now my 07 does this: starts right up, idles fine, air screws about 2.5 out on all 4 carbs, (even though Ive heard the back carbs should be turned out differently) as you accelerate, it revs thru the range ok, no stumbling, but if your at a steady state cruise, in a lower gear, it pops abit, you can roll the throttle to get out of it, change gears, but you can hear and feel the slight pop and somewhat of a stumble. Ive synched the carbs, chkd the plugs to make sure they are seated, clamps to the air box and carb boots are gtg. not sure what else to do other than tear the carbs apart and starts there. any thoughts?

 

[veebooster]

Remove your air filter and check that your needles are moving freely. I used a screw driver to reach in and move each slide. Of course be gentle. One needle was hanging up and causing a backfire as you describe.

 

[Fire-medic]

Remove your air filter and check that your needles are moving freely. I used a screw driver to reach in and move each slide. Of course be gentle. One needle was hanging up and causing a backfire as you describe.

Trying to force a stuck slide will often result in a broken throttle slide. It's necessary to use a good solvent to try to break-down any deposits holding the slide immobile, and if you cannot do it with the carburetors mounted, remove the rack and do it on the bench. Slides are >$100 apiece.

 

[veebooster]

Trying to force a stuck slide will often result in a broken throttle slide. It's necessary to use a good solvent to try to break-down any deposits holding the slide immobile, and if you cannot do it with the carburetors mounted, remove the rack and do it on the bench. Slides are >$100 apiece.

Good advice. My slide wasn't stuck. The needle was hanging up. Readjusted and moved it to another carb. Backfire solved.

 

[racerboy]

mine are moving freely, no stiction. Im selling it!

 

[racerboy]

Its never ending. Now my 07 does this: starts right up, idles fine, air screws about 2.5 out on all 4 carbs, (even though Ive heard the back carbs should be turned out differently) as you accelerate, it revs thru the range ok, no stumbling, but if your at a steady state cruise, in a lower gear, it pops abit, you can roll the throttle to get out of it, change gears, but you can hear and feel the slight pop and somewhat of a stumble. Ive synched the carbs, chkd the plugs to make sure they are seated, clamps to the air box and carb boots are gtg. not sure what else to do other than tear the carbs apart and starts there. any thoughts?

Well, finally found the problem, apparently, during one of my many needle chge outs, a set of Calif. spec needles ended up in the beast, so I swapped them out and conducted a before & after, solved.