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Thread: The bike is backfiring!!!

  1. #1
    Administration Big Kahuna's Avatar
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    Default The bike is backfiring!!!

    My bike has begun to backfire when I get off the throttle at low speed. Most of the time it kind of grumbles like it's loading up but every once and a while it really let's one a loud pop. It's never done this before and I haven't changed anything in the carbs or the engine.

    Any ideas?
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  2. #2
    RRzone Elder xraycatj's Avatar
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    Default Re: The bike is backfiring!!!

    I just glanced at the manual and got this (word for word):

    Afterburn when engine braking is used:
    1. lean mixture in slow circuit
    2. air cut-off valve malfunction
    3. emission control malfunction
    -secondary air supply system faulty
    -loose, disconnected, or deteriorated hoses of emission control sys.

    Backfire or misfire during acceleration:
    1. ignition system malfunction (like my dead battery)
    2. fuel mixture too lean
    Hidden Content Fortunately I keep my feathers numbered for just such an occasion. Hidden Content

  3. #3
    Administrator Brent's Avatar
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    Default Re: The bike is backfiring!!!

    Just bring it up to Factory and pay them to tune it..... trust me - my 94F2 did that - it was to have to do with improper carb settings...

  4. #4
    RRzone Elder Calkidd's Avatar
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    Default Re: The bike is backfiring!!!

    Lean fuel mixture?

    I thought backfireing had to do with excessive fuel in the exhaust pipes igniting?
    CalKidd
    "Eating and sleeping are the only activities that should be allowed to interrupt a man's enjoyment of his cigar" - Mark Twain

  5. #5
    RRzone Elder 66droptop's Avatar
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    Default Re: The bike is backfiring!!!

    Quote Originally Posted by Calkidd
    Lean fuel mixture?

    I thought backfireing had to do with excessive fuel in the exhaust pipes igniting?
    I thought popping under load was from lean conditions. Actually, I know this. But I thought that popping under no load (engine braking, et cetera) was from being rich. Not 100% sure on the second part.

  6. #6
    Administration Big Kahuna's Avatar
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    Default Re: The bike is backfiring!!!

    It's strange, You wouldn't notice any problem the way the engine runs. It's still strong and I get no hesitation under throttle or idle.

    I had an exhaust leak once, and I could feel it under acceleration, but this backfiring thing is different. It only does it when I release the throttle. If I ride long enough, It will start to do it in between shifts if I'm running it hard and high in the RPMs.

    By the way, I jumped on it last night when a guy in a vette tried to get silly when leaving a signal light and I was again reminded how slow those cagers really are.
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  7. #7
    Administrator Brent's Avatar
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    Default Re: The bike is backfiring!!!

    Bad Gas?
    Lean?
    Exhaust Leak?
    All of the above?

  8. #8
    RRzone Elder Blademan's Avatar
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    Default Re: The bike is backfiring!!!

    I have always had small backfiring under heavy engine breaking since I put the two bro's jet kit in
    When life hands you lemons . . . cut'em up . . . put'em in a Corona . . . and drink. Problem solved !! Hidden Content

  9. #9
    RRzone Elder 66droptop's Avatar
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    Default Re: The bike is backfiring!!!

    Probably your exhaust bearings. And we all know that means your bike is F-ed up now. Should probably just part it out. Let me try to remember what mods your bike has that I'm interested in... Well there's the clear tail light. I remember that part. You should probably just give it to me for free since I diagnosed your problem and saved you all that time, effort, and money. Oh, and also because not since Steve McQueen has the world seen someone as cool as me. I'll PM you my address so you know where to ship it.

  10. #10
    Administrator Brent's Avatar
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    Default Re: The bike is backfiring!!!

    Quote Originally Posted by Blademan
    I have always had small backfiring under heavy engine breaking since I put the two bro's jet kit in

    Blademan - this could be from an air leak.... in the exhaust system... might want to check that...

    If I rememebr they used to package hi-temp silicon for this issue

  11. #11
    Administration Big Kahuna's Avatar
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    Default Re: The bike is backfiring!!!

    Quote Originally Posted by 66droptop
    Probably your exhaust bearings. And we all know that means your bike is F-ed up now. Should probably just part it out. Let me try to remember what mods your bike has that I'm interested in... Well there's the clear tail light. I remember that part. You should probably just give it to me for free since I diagnosed your problem and saved you all that time, effort, and money. Oh, and also because not since Steve McQueen has the world seen someone as cool as me. I'll PM you my address so you know where to ship it.
    Damn, it can't be those stupid exhaust bearings... I've replaced those twice already.
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  12. #12
    Administration Big Kahuna's Avatar
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    Default Re: The bike is backfiring!!!

    Okay, I pulled the main hose that goes from the PAIR valve to the airbox. The PAIR valve is suppose to control the flow of fresh air to the intake. When I pulled the hose, nothing changed but when I plugged the hose with my thumb, the backfiring stopped. It seems the PAIR valve must be stuck open thus continuously feeding the intake with too much fresh air.

    Mystery solved. I decided to pull the remaining smog crap off as I've already removed the clogged evap canister. I need to find some smog block off plates. I know Two Brothers used to carry them.

    How about it Brent, can you hook me up. I know you have connections at Two Brothers.
    If you can't find anything nice to say… Don't say anything nice at all.

  13. #13
    RRzone Elder 66droptop's Avatar
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    Default Re: The bike is backfiring!!!

    Quote Originally Posted by Big Kahuna
    Okay, I pulled the main hose that goes from the PAIR valve to the airbox. The PAIR valve is suppose to control the flow of fresh air to the intake. When I pulled the hose, nothing changed but when I plugged the hose with my thumb, the backfiring stopped. It seems the PAIR valve must be stuck open thus continuously feeding the intake with too much fresh air.

    Mystery solved. I decided to pull the remaining smog crap off as I've already removed the clogged evap canister. I need to find some smog block off plates. I know Two Brothers used to carry them.

    How about it Brent, can you hook me up. I know you have connections at Two Brothers.
    Wait. We have that crap on 900s? I thought it was just those newfangled bikes with EFI and that mishmash. Stone tools were cutting edge back when the 900 was made.

  14. #14
    RRzone Elder Blademan's Avatar
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    Default Re: The bike is backfiring!!!

    Quote Originally Posted by 66droptop
    Wait. We have that crap on 900s? I thought it was just those newfangled bikes with EFI and that mishmash. Stone tools were cutting edge back when the 900 was made.
    Never knew either
    When life hands you lemons . . . cut'em up . . . put'em in a Corona . . . and drink. Problem solved !! Hidden Content

  15. #15
    Administration Big Kahuna's Avatar
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    Default Re: The bike is backfiring!!!

    It's true!!! Would I lie to you guys?
    If you can't find anything nice to say… Don't say anything nice at all.

  16. #16
    RRzone Elder Blademan's Avatar
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    Default Re: The bike is backfiring!!!

    OK so he does make a good point . . . !!!!
    When life hands you lemons . . . cut'em up . . . put'em in a Corona . . . and drink. Problem solved !! Hidden Content

  17. #17
    RRzone Elder wingnut1's Avatar
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    Default Re: The bike is backfiring!!!

    This is a California specific Mod most bikes in the us will not have it....

    this is due to Californias emission standards
    Leon Carney

    98 cbr 900rr (SSSA, custom GP exhaust, front end conversion)
    01 Ducati 748s

  18. #18
    Not been here that long gingerrific's Avatar
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    Default Re: The bike is backfiring!!!

    I have the same problem!!! But mine is lots of little pops!!! Just bought the bike as well he putca commander on it how do I remove it cause they fo no good on carb bikes

  19. #19
    Not been here that long SIXDOG's Avatar
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    Default Re: The bike is backfiring!!!

    I have the same issue on decel...it usually starts popping at about 4K to about 2.5k...Mike Nixon ( CBX carb tuner guru ) has a CBX carb tunning book that identifies that issue as a lean idle screw mixture. I backed off the screws about 3/4 of a turn and it cured the issue.
    07 CBR1000RR Repsol
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  20. #20
    RRzone Member
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    Default Re: The bike is backfiring!!!

    Quote Originally Posted by gingerrific View Post
    I have the same problem!!! But mine is lots of little pops!!! Just bought the bike as well he putca commander on it how do I remove it cause they fo no good on carb bikes
    You seem to have asked the same question in at least 3 threads! I've replied on one .....
    Dave
    Carpe diem ...

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