Xt200 Problem challenge!
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Thread: Xt200 Problem challenge!

  1. #1
    Junior Member Bikesarebetter's Avatar
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    Xt200 Problem challenge!

    I’ve made a mild custom xt200. The engine is nearly identical to the TW. I’ve been chasing a few issues and think I have it narrowed to one.

    The bike idles perfect when hot, and at Full Throttle it is shockingly fast. No misfires, just smooth.

    But, at 1/8-1/4 throttle, the RPMs jump quickly up and down +/- 1500 with occasional misfires.

    Recently replaced primary coil. The stator and pickup coil resistance is within spec. I replace the CDI with a new one and it got slightly worse(possibly more aggressive advance?).

    Every connection has been cleaned and dielectric applied. Tried different plugs. Valves are good. Triple checked for intake leaks.

    This problem has developed over a week of riding. Before this, I was extremely happy with my set up: K&N filter, vm26 with 17.5 pilot and 190 main, stainless xt 225 header, I cut up a brand new FMF And added a “power bomb” 30” down the pipe from the exhaust valve. When it runs, It feels like my old xr250! Smooth aggressive torque with occasional popping on deceleration.

    I’m ready to chuck it off a cliff. Help.
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    Junior Member Bikesarebetter's Avatar
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    Some more pictures just because I think it looks cool
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    Senior Member ejfranz's Avatar
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    Hopefully Kris (Admiral) chimes in as he has the same bike.
    2001 TW200 sporting a MT43 up front. Duro has gone to a good home. 2015 VStrom XT, 1996 DT 200, Broken 2010 Xingue 400 XY. 2009 WR250r now shared with my son.

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    Senior Member elime's Avatar
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    My guess is its the carburetor. Take it apart and clean it. If you gets the smallest speck of dust stuck in the pilot jet the engine runs very poorly. Open the idle mixture screw a turn or two and see what happens. Perhaps if you have a backup carb give it a try. Good luck. Remember to report back what it was. We all learn from the experiences of others.
    Long live the internal combustion engine!

  6. #5
    Senior Member SHAG's Avatar
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    I would look for an intake air leak
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    Go like hell, You'll get there quicker!
    05-BMW1200GS- Rock Red 106k miles
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  7. #6
    Senior Member admiral's Avatar
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    Quote Originally Posted by Bikesarebetter View Post

    This problem has developed over a week of riding. Before this, I was extremely happy with my set up: K&N filter, vm26 with 17.5 pilot and 190 main, stainless xt 225 header, I cut up a brand new FMF And added a “power bomb” 30” down the pipe from the exhaust valve. When it runs, It feels like my old xr250! Smooth aggressive torque with occasional popping on deceleration.
    Popping on decel usually means the engine is running lean. With a less restrictive air filter and less restrictive exhaust, the air (mostly) is flowing through the system faster possibly causing a lean condition. By changing the air filter and exhaust you most likely have to still tune your jetting. I have no idea what a "power bomb" is. What does your sparkplug color look like?

    To clarify, the XT ran fine before you made the above changes? Did it have a stock air cleaner and exhaust before the above changes? Is the carb different than stock? As elime mentioned, most likely a carb issue (jetting). I'm not very familiar with carburetor sizes but you must have a different size carb than my '83 XT as your pilot and main jet numbers are way different than stock XT and my XT. Stock is something close to 40 pilot and 122. My XT with the Super Trapp is at 40-112.

    When I got my 83 XT it came with an aftermarket Super Trapp muffler. The engine was running very rich with the stock air cleaner and aftermarket exhaust. I had to drop the main jet down before it started running correctly. I had to experiment with the jetting and it took several changes before it got dialed in. I took small steps to make sure I didn't go too far and lean it out. My issue was engine stumble at half-throttle and more pronounced in 4th and 5th gears. Started and idled ok and ran fine at slower speeds.

    I see you've also gotten rid of the electricals (or most of them anyway). Just an observation not related to the issue.
    grewen likes this.
    Hidden Content A ride in the woods helps me relax and release tension. The fact I'm dragging a body should be entirely irrelevant?

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    Senior Member Rider21's Avatar
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    Quote Originally Posted by SHAG View Post
    I would look for an intake air leak
    I second that.
    Beauty is as beauty does.
    If it works good, it's beautiful.

  9. #8
    Senior Member admiral's Avatar
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    He did say he "triple checked for air leaks" so I discounted that but worthy of the mentions again. That would then make it a quadruple or more check for air leaks?
    Hidden Content A ride in the woods helps me relax and release tension. The fact I'm dragging a body should be entirely irrelevant?

  10. #9
    Junior Member Bikesarebetter's Avatar
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    Update! This is a great example of electric issues presenting as Carburetion problems.

    When I check the timing with a timing light, the advance is bouncing around erratically at lower rpm. It’s consistent with no advance at low idle, and advance at high RPM, but 1000-2000 it is chaos.

    I have tried a new CDI, different coil, different coil caps, different plugs...

    The only thing I can’t replace is the pickup coil, as they are not made any longer. It has the proper resistance and it’s a simple Hall effect sensor and they “never” go bad.

    I’m still stumped. Next step is re wire the whole bike I guess? Or chuck it in the lake?

  11. #10
    Junior Member Bikesarebetter's Avatar
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    It’s hard to hear in the video because of the open case, but the rpm’s are bouncing around in sync with the timing mark disappearing.

    https://youtu.be/jUNHxYNhWPE
    Last edited by Bikesarebetter; 05-23-2019 at 10:53 AM.

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