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Thread: Backfiring

  1. #1
    Member ebikerman's Avatar
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    Fellow riders,



    After all the carb work done on my '06 TW200 I am having a new problem now. Work done on my carb by an experienced motorcycle mechanic included cleaning, replacing a broken pilot jet (damaged by previous owner), replacing the enrichner circuit plug (also misplaced by original owner) and adjustment of the idle mixture screw. Before all this my bike would not run without the enrichner being on. After the repairs the bike would not run with the enrichner on, hot or cold. Finally that was fixed when the mechanic found that the enrichner ciruit plug was missing and replaced it. But, the bike then ran a little lean to the point of detonation on hard excelleration. That was fixed by adding a single shim under the needle. The bike runs great now, but a new problem has begun....it backfires on deceleration....mostly a rumbling, but at times a mild backfire. What do we need to do now? My intention is to try to stay within EPA standards. H E L P !!!



    Thanks, Dan

  2. #2
    Senior Member assquatch20's Avatar
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    It's just one of those things, most of the time. If your valves are adjusted right, cam chain is right, plug comes out right at varying chops, just live with it. If you get timing perfect and have a rich condition on the plug at a certain throttle range, fine-tune that jet.

  3. #3
    Senior Member LittleCowTW's Avatar
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    Quote Originally Posted by Dan P View Post
    Fellow riders,



    After all the carb work done on my '06 TW200 I am having a new problem now. Work done on my carb by an experienced motorcycle mechanic included cleaning, replacing a broken pilot jet (damaged by previous owner), replacing the enrichner circuit plug (also misplaced by original owner) and adjustment of the idle mixture screw. Before all this my bike would not run without the enrichner being on. After the repairs the bike would not run with the enrichner on, hot or cold. Finally that was fixed when the mechanic found that the enrichner ciruit plug was missing and replaced it. But, the bike then ran a little lean to the point of detonation on hard excelleration. That was fixed by adding a single shim under the needle. The bike runs great now, but a new problem has begun....it backfires on deceleration....mostly a rumbling, but at times a mild backfire. What do we need to do now? My intention is to try to stay within EPA standards. H E L P !!!



    Thanks, Dan
    The condition you describe is called lean idle popping. It happens when the mixture is too lean on decel. The easiest thing for you to do would be to check the position of your pilot screw. I believe it is supposed to be between 1 1/2 and 2 1/2 turns out. bottom line is carb tuning is tricky. if you take that screw out another half turn it might fix the issue. if not your mechanic will have to rebaseline your carburetor. likely including main jet, needle shim and pilot jet in that order. But it should be easy for you to check your pilot screw assuming your mechanic already pulled out the brass acess plug that they put in at the factory.
    Persistence is the better part of genius.

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  5. #4
    Member ebikerman's Avatar
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    LittleCowTw, Thanks for great information. Strange my mechanic did not mention this condition. I had another bike (Suzuki 650 single) that had a small diaphragm device to add fuel during deceleration to stop all that backfiring....The TW200 may have this device too. Strange it did not do that backfiring before he added the shim and closed off the enrichner curcuit chanel that was supposed to be closed. Looks as if that would have made things richer. My TW backfires less after warmed up and less today that was warmer than yesterday. The warmer condition added to your info and including Suzuki setup sure makes what you said reasonable. I will talk to the mechanic soon. It really is nice to have a mechanic that is your friend. Thanks so much, Dan

  6. #5
    Senior Member jbfla's Avatar
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    Quote Originally Posted by Dan P View Post
    ...I had another bike (Suzuki 650 single) that had a small diaphragm device to add fuel during deceleration to stop all that backfiring.... Dan
    The TW has that circuit also.



    The decel popping can also be caused by an air leak in the exhaust system.



    Jb
    2018 Triumph Street Twin..............2016 CB500F
    2014 XT250 ..................................2008 H-D Softail Deluxe
    2008 SV 650..................................2007 DR 650..

  7. #6
    Senior Member jbfla's Avatar
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    Double post...
    2018 Triumph Street Twin..............2016 CB500F
    2014 XT250 ..................................2008 H-D Softail Deluxe
    2008 SV 650..................................2007 DR 650..

  8. #7
    Senior Member LittleCowTW's Avatar
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    Quote Originally Posted by jbfla View Post
    The TW has that circuit also.



    The decel popping can also be caused by an air leak in the exhaust system.



    Jb
    JB is right, it could be any number of things causing your popping, I should have led with that. Troubleshooting your bike by adjusting your pilot screw is not advised by the factory, hence the brass plug blocking it. But seeing as how your carburetor is modified you might have luck with that screw.
    Persistence is the better part of genius.

  9. #8
    Senior Member jbfla's Avatar
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    Quote Originally Posted by LittleCowTw View Post
    Troubleshooting your bike by adjusting your pilot screw is not advised by the factory, hence the brass plug blocking it. But seeing as how your carburetor is modified you might have luck with that screw.
    LittleCowTW,



    ...I don't intend to be rude, but (IMO) on the TK carb for the TW, adjusting the pilot screw is a necessity in all but the most extreme cases (high altitude).



    The factory setting is extremely lean for emissions purposes. Adjusting the pilot screw is a necessary step in tuning the carb for your location.



    jb
    2018 Triumph Street Twin..............2016 CB500F
    2014 XT250 ..................................2008 H-D Softail Deluxe
    2008 SV 650..................................2007 DR 650..

  10. #9
    Senior Member LittleCowTW's Avatar
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    Quote Originally Posted by jbfla View Post
    LittleCowTW,



    ...I don't intend to be rude, but (IMO) on the TK carb for the TW, adjusting the pilot screw is a necessity in all but the most extreme cases (high altitude).

    A

    The factory setting is extremely lean for emissions purposes. Adjusting the pilot screw is a necessary step in tuning the carb for your location.



    jb
    No not at all, you make an excellent point. And frankly the pilot screw is almost always a first step for me with a stock setup. I only intended to point out that factory manuals tend to recomend that the causes of lean conditions be discovered and treated before we start fiddling with our adjustments. I have an old bike that got lean after the exhaust corroded internally and started disintegrating. Your post about exhaust leaks made me rethink my original advice. Furthermore there is no end to what I don't know so I don't fear the possibility of getting educated :-)
    Persistence is the better part of genius.

  11. #10
    Senior Member jbfla's Avatar
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    Quote Originally Posted by LittleCowTw View Post
    No not at all, you make an excellent point. And frankly the pilot screw is almost always a first step for me with a stock setup. I only intended to point out that factory manuals tend to recomend that the causes of lean conditions be discovered and treated before we start fiddling with our adjustments..... Your post about exhaust leaks made me rethink my original advice.
    I do more than a bit of rethinking myself.



    The most common cause of lean running on TW is the factory setting of the pilot screw.



    On a bike that has be sitting, it can be clogged carb passages,, jets, ... manifold air leaks, ...



    I saw the picture of your TW without the air box. I realize you have the older TK carb, but am curious as to the jet size and pilot screw setting.



    Jb.
    2018 Triumph Street Twin..............2016 CB500F
    2014 XT250 ..................................2008 H-D Softail Deluxe
    2008 SV 650..................................2007 DR 650..

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