Won't start just the occasional back fire???? HELPPPPP PLEASE
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Thread: Won't start just the occasional back fire???? HELPPPPP PLEASE

  1. #1
    Junior Member puzzled1's Avatar
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    Won't start just the occasional back fire???? HELPPPPP PLEASE

    Hi guys.

    I'm having a hell of a time trying to get my tw200 running, I have set the timing and valve clearances following the instructions in the manual and all I am getting is the starter turning over and the occasional back fire. I would appreciate any and all help that I can get. Thanks .

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    Super Moderator littletommy's Avatar
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    Welcome to the forum! We'll try to help if we can. It would help if you shared with us the year of the bike and any past history that you know of. What were the settings you used? Did the bike sit awhile? If so, how does the tank look? Old gas? Information from the previous owner if you just got it and are trying to get it running? Things like that....
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    Senior Member elime's Avatar
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    How did it run before you adjusted it?
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    Senior Member Fred's Avatar
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    Backfire through carb or tailpipe? More details please as requested above.
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    Senior Member admiral's Avatar
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    Had the engine bee taken apart and put back together (cam chain timing)?
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    Junior Member puzzled1's Avatar
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    The back fire is coming out of the pipe not the carb, the gas is fresh and tank is 100% clean, engine was rebuilt by a mate, and have been told it is set correctly, if anyone has any detailed instructions on how set the cam chain timing so i can pull everything apart and check i would be most gratefull.

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    Super Moderator Purple's Avatar
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    Senior Member fishguy's Avatar
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    Double check the timing and valves. It is possible to "time" the engine incorrectly and set the valves on the wrong rotation. I know, I have done it.

    So, when timing, you MUST know when the piston is at TDC on the compression stroke. Remember, the flywheel goes around twice for each complete engine cycle (compression/combustion/exhaust/intake). If you line-up the timing marks when engine is on the "exhaust/intake" cycle and set the valves, all kinds of strange shit happens -- back-fires being one.
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  10. #9
    Senior Member admiral's Avatar
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    Quote Originally Posted by puzzled1 View Post
    The back fire is coming out of the pipe not the carb, the gas is fresh and tank is 100% clean, engine was rebuilt by a mate, and have been told it is set correctly, if anyone has any detailed instructions on how set the cam chain timing so i can pull everything apart and check i would be most gratefull.
    Quote Originally Posted by fishguy View Post
    Double check the timing and valves. It is possible to "time" the engine incorrectly and set the valves on the wrong rotation. I know, I have done it.

    So, when timing, you MUST know when the piston is at TDC on the compression stroke. Remember, the flywheel goes around twice for each complete engine cycle (compression/combustion/exhaust/intake). If you line-up the timing marks when engine is on the "exhaust/intake" cycle and set the valves, all kinds of strange shit happens -- back-fires being one.

    puzzled1, fishguy mentions a little better what I was trying to say with the cam timing. No way to tell if this is the problem, but you can verify the cam chain timing fairly easy. I'll post a video from forum member B-Dub from the Technical Write-ups in the Technical Sticky thread when he re-timed his engine after replacing the base gasket.

    In words, you will check the cam chain sprocket mark and the flywheel timing marks are lined up properly. This video shows that very well, so here goes. On post #38, page 4 of the thread is the description B-dub wrote for timing. In your case, you just need to verify and rule this out as a culprit of the backfiring.







    Also, as fishguy mentioned, you also need to verify the valves are adjusted properly. ...and you need to make sure your carburetor is set correctly. For instance; my new 2015 TW has been backfiring on decel since new. I know the carb pilot screw (fuel mixture) is set to be lean from the factory. Last night I adjusted the pilot screw which eliminated 99% of my backfiring. I removed the plug on the bottom side of the carb exposing the pilot screw. The pilot screw was set at 1-1/2 turns out. I then turned it out too 2-1/2. This is a good starting point when making this adjustment. I went for a test ride and no more backfiring on decel, so I think it's good to go. I will continue to monitor and make sure this is the setting I should leave it at. I'll check the spark plug to make sure I'm not to lean or to rich, but based on my past experience from my old TW, I'm pretty confident this is the right setting for me.

    Here are a couple photo's showing the location of the pilot screw. First one is with the plug in and the second out exposing the screw. Give thanks to jbfla for these picture's.





    Hope this helps in finding your backfiring cause. Backfiring can be caused by many things including electrical problems, but making sure timing, valves set, and proper carb tuning usually cures it. Good luck.
    Last edited by admiral; 08-26-2015 at 01:23 PM.
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  11. #10
    Junior Member puzzled1's Avatar
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    Thanks guys, I'm due for a day in the workshop next week, will have a look,check and come back to you with a status update.

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