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Discussion in 'Technical and Troubleshooting Torque' started by firefling, Dec 4, 2005.

  1. I had my spark plugs changed on Saturday and next day noticed that sometimes when I've rolled off the throttle and letting the bike cruise, it would backfire. What causes this and how can I fix it?

  2. i think somethings broken fling

    i'll bring the spanner..
  3. The meaty Popping and backfire sounds through the exhaust when you roll off the throttle are dead sexy, it’s the best part of coming up to a bunch of cages and having your exhaust behave like a violent junkyard dog whilst lane splitting to the front.
    Don’t know why your concerned fling, enjoy it.

    Technically I know of 2 reasons it happens –

    1. You are running a lean mixture.
    2. You run straight out pipes with no baffles which cause a reverse pressure wave through the exhaust system.
  4. From what I undestand what causes backfiring, one is that unburnt fuel being burnt up in your exhaust just as it exits the exhaust ports, causing the back firing, have to agree with duhast on that, sounds menacing, maybe your plugs to hot or cold? :?
  5. Which one is it? Too hot or too cold? I've heard the theories on why it happens but how do I fix it?
  6. One of your plug caps could be loose or simply making a poor connection, this is the most likely scenario, unless you have had a faulty plug installed.
  7. Dunno about that. If it's a single plug related issue, why only on the overrun? I'm not ruling it out, but on balance I'm with the 'running slightly lean' crowd.

    Does the bike have a choke?
  8. I'm with thcpt on this one. I would have thought backfiring occurs when you have unburnt fuel, usually when running too rich as opposed to too lean. Dunno how changing plugs could affect you A/F ratios though. :?:
  9. I cracked the choke on about half and gave it a 1/4 twist the other day in my haste. When I hit the starter it sounded like a WMD going off. (narrow lane, big buildings). Opps off the throttle and no dramas. Too rich a mix I my case :shock: I left before the cops could arrest me and beat a WMD confession out of me "Yes, Yes my names Achmed just stop hitting me!" :p
  10. I only suggested it because I have had this very same problem and it stands to reason that if the only variable here is that the plugs have been replaced, then it probalby has something to do with that process.

    I would be interested to hear whether this is the case firefling?
  11. Sounds like lean-out....
    2 general areas to look at:
    intake (yours was a carb-model?): one of the rubber intake boots has come loose (slipped clamp?)

    exhaust side:
    header-pipe bolts/ nuts or one of the exhaust clamps has come loose (check for black carbon blow-by around all joints)

  12. You can get this if you put too hot a plug in. So check the right ones went in. Replace them with the right temperature ones

    Check all leads for shorts and good connection.

    Also from memory to lean backfires through the carbs.

    Rich backfires through the exhaust. But wwhy would the bikes mixture change just because you changed the plugs? Did you disturb much when the plugs were changed? Check vacuum lines.
  13. The silence is deafening Firefling........