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BackFiring?

Discussion in 'FZR250.com - Archives' started by FolCan, Jan 8, 2006.

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  1. FolCan

    FolCan Active Member

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    Hi

    I have noticed that when slowing down.. using the Gears my bike has started backfiring...

    Im told that it might be holes in the exuast
     
    FolCan, Jan 8, 2006
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  2. TBone

    TBone New Member

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    Here are some more thoughts:

    running bit rich??

    Carbon built up in headers??

    valves not sealing properly??

    And my favorite... EXUP valve out of tune...

    (if it is a leaky exhaoust than start looking around the EXUP valve and where the end can meats the headers)
     
    TBone, Jan 8, 2006
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  3. Ciaran

    Ciaran New Member

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    And try replacing the header gaskets, if they aren’t sealing properly they can have that effect.
     
    Ciaran, Jan 8, 2006
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  4. raaqi

    raaqi New Member

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    I noticed when on the track and reving hard, if you down gear and the revs are high it'll backfire. This is normal but you shouldn't get alot of backfiring if you're road riding...

    If I see a bunch of people on the side of the road, I always down gear, keep the revs up, then hit the kill switch, wait a second, pop it back on and BANG! You'll get a nice backfire and scare the crap out of the people on the side of the road. Funny stuff. Ehehe
     
    raaqi, Jan 8, 2006
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  5. FolCan

    FolCan Active Member

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    Well I need to fix some rust on the headers sometime so ill be able to check it for Carbon build up

    how would you know if the exup is out of tune?

    I suspect Carbon build up though... because it just started doing it about a week ago.. and it never did it before then
     
    FolCan, Jan 9, 2006
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  6. koma

    koma New Member

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    My bets are on that your air filter needs cleaning / replacing.
    My little FZR used to start burbling (back firing on over run) when ever it's air filter needed cleaning. Cleaning and re-oiling the air filter would fix it up straight away.

    The other options would definitely be carbon buildup; but it really depends if it's just a light popping or burbling on over run or if it really is a serious back firing.
     
    koma, Jan 9, 2006
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  7. dave

    dave Well-Known Member

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    Air leaks at the exhaust headers will cause a popping/backfiring sound on overrun as fresh air is sucked in to the exhaust. This used to be a real problem if a good seal was not obtained when putting extractors and sports exhaust on car engines.
     
    dave, Jan 9, 2006
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  8. FolCan

    FolCan Active Member

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    Its not serious backfiring.. you can barely hear it backfiring

    Update: I dont think its a hole in the exaust.. as I blocked the exaust to see if I could hear it leaking out anywhere and it starts stalling the bike indicating that its building up pressure.. perhaps its carbon build up... maybe I need to check the carbs
     
    FolCan, Jan 9, 2006
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  9. FolCan

    FolCan Active Member

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    Ok I checked the Air Filter and my father says its alright still... But I did notice Dust was getting through from somewhere.. so I cleaned it up and Sealed where I thought it might have been getting through


    OH and while doing that I noticed my petrol tank Full of rust.. it seems the seal in the petrol cap has stopped working <!-- s:( --><img src="{SMILIES_PATH}/icon_sad.gif" alt=":(" title="Sad" /><!-- s:( -->
     
    FolCan, Jan 10, 2006
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  10. Starter

    Starter New Member

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    It's backfiring cause it's running LEAN through that rev range. It's running lean through that portion of the rev range most probably due to a slightly out of adjustment exup valve or there is gunk in a carbie impeading the flow of fuel. I would start on the Exup. A lot easier and quicker. Most 4cyl bikes will exhibit this kind of behavour when a freer flowing exhaust is fitted, and twins for the same reason or lumpy cams.
     
    Starter, Jan 10, 2006
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  11. FolCan

    FolCan Active Member

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    Ill have a look at teh exup then... another thing that come to mind is the last time I checked the Spark Plugs they were quite worn.. perhaps some new Spark Plugs is in order
     
    FolCan, Jan 10, 2006
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  12. FolCan

    FolCan Active Member

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    OK it seems it was the air Filter

    Because I gave it a clean yesterday and now it doesnt seem to be backfiring anymore.. and it seems to be generally running better

    Thanks for all the help
     
    FolCan, Jan 11, 2006
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  13. koma

    koma New Member

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    I love being right.
    <!-- s:lol: --><img src="{SMILIES_PATH}/icon_lol.gif" alt=":lol:" title="Laughing" /><!-- s:lol: -->

    Good to hear it's running properly again.
     
    koma, Jan 11, 2006
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  14. FolCan

    FolCan Active Member

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    I took it on a long ride on the motorway.. First time the bike has been above 70kmh since I got it

    Was good fun
     
    FolCan, Jan 11, 2006
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  15. FolCan

    FolCan Active Member

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    Argh

    It started doing it again lol

    Im gonna try check the EXUP now

    The EXUP is in tune so theres no problems there
     
    FolCan, Jan 12, 2006
    #15
  16. biglez

    biglez New Member

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    Care to retract Koma?
    <!-- s:roll: --><img src="{SMILIES_PATH}/icon_roll.gif" alt=":roll:" title="Rolling LoL" /><!-- s:roll: --> <!-- s:roll: --><img src="{SMILIES_PATH}/icon_roll.gif" alt=":roll:" title="Rolling LoL" /><!-- s:roll: --> <!-- s:roll: --><img src="{SMILIES_PATH}/icon_roll.gif" alt=":roll:" title="Rolling LoL" /><!-- s:roll: -->
     
    biglez, Jan 13, 2006
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  17. koma

    koma New Member

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    Nope. <!-- s:rofl: --><img src="{SMILIES_PATH}/icon_razz.gif" alt=":rofl:" title="Rofl" /><!-- s:rofl: -->

    I stand by my comment that the 'first' thing i would've checked was the air filter. Thats just going from my experience with my FZR250.

    Failing that i'd move onto things like carb balance, float heights, idle mixture settings, and as previously mentioned... EXUP.
     
    koma, Jan 13, 2006
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  18. TiMBuS

    TiMBuS New Member

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    Wow today I took it to the rego branch to reg mine.. On the way back felt a bit pissed off so I blatted it to check the rev range. So technically the day I first legally rode it I got it over 70.. In fact I think I got it over 110...

    You gotta take it to a nice long curvy stretch, man. Then see how much you worry about the backfiring.
     
    TiMBuS, Jan 13, 2006
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  19. FolCan

    FolCan Active Member

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    Well Ive checked the EXup and Air Filter...

    I think I may have found whats causing it... theres a bad spark plug cap its all taped up with masking tape so perhaps its stopping that cynlinder from working sometimes or something I dunno

    Ill have a look into it this weekend
     
    FolCan, Jan 13, 2006
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  20. TiMBuS

    TiMBuS New Member

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    Test the spark plug. See if it sparks consistantly. Wiggle the lead while you test for spark and see if it skips at all.

    Also, run the bike for a few seconds till the exhaust headers warm up, then feel each pipe to see if it's warm. Make sure they're all the same temperature. If not, then you have a faulty cap.

    Also, do you know if the bike is running particulary rich or lean? You haven't said. Does it blow a little bit of visible smoke from the exhaust when you rev it from idle?
     
    TiMBuS, Jan 13, 2006
    #20
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