CDI Box and performance
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  1. #1
    Junior Member Riverman1962's Avatar
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    Anyone able to answer a technical question about the CDI Box. Have 1987 TW200 and CDI Box developed a glitch...uable to accelerate beyond idle. Bypassed (disconnected brown, I think--not in front of me?) wire and bike accelerates. Did some other things to her and took a couple of months to get her on the road. Question: If the CDI circuitry is defective, would this affect the power? She does not seem to be as powerful now. Only goes about 50 mph comfortably...and I even put the smaller 44 tooth rear sprocket on...? Does this seem right?

  2. #2
    Senior Member pgilles's Avatar
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    Can't help with the CDI questions, but...

    1) Is the carb clean after sitting for a couple months? Good/new fuel?

    2) Did the bike have the 44 on it before the CDI issue? Or was that added during those couple months down time which would make it tough to compare apples to apples?

    3) Being winter time and not knowing where you live, is the temperature the same now as it was a couple months ago? If not, jetting could be causing a power issue.



    Even with the 44, it should pull over 50mph. I'll let the electrical guys take it from here...
    Sold bike.



    Youtube vids of old TW's acceleration:

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  3. #3
    Junior Member Riverman1962's Avatar
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    Quote Originally Posted by pgilles View Post
    Can't help with the CDI questions, but...

    1) Is the carb clean after sitting for a couple months? Good/new fuel?

    2) Did the bike have the 44 on it before the CDI issue? Or was that added during those couple months down time which would make it tough to compare apples to apples?

    3) Being winter time and not knowing where you live, is the temperature the same now as it was a couple months ago? If not, jetting could be causing a power issue.



    Even with the 44, it should pull over 50mph. I'll let the electrical guys take it from here...

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  5. #4
    Junior Member Riverman1962's Avatar
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    First off, thanks Pgilles.

    Answers:

    1) bike is clean with fuel--replaced head gasket and went thru bike--MCI instuctor oversaw/did most work--no questions about competency...he diagnosed bad CDI box...whereby we bypassed brown wire to allow acceleration.

    2) went from 50 teeth to 44 teeth...which would notionally give me better top end MPH...not so. Am still giving her the somewhat 10 hrs of genter break in after replacing rings and honing...This bike does not want to push past 50 and it doesn't seem right.

    3) can revisit jetting...twas FL before the fixes and FL after....total carb rebuilds...again under jedi mechanic.



    Thanks for anything anyone else can offer...again....mechanic diagnosed bad wire in CDI box...bipassed and advised me of suspect performance. Am thinking I have enough to justify a new CDI but wanted to check.

  6. #5
    Senior Member uktw125's Avatar
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    I must say I am no expert on electrics but I do know the CDI controls the ignition advance curve. That is the faster the engine spins the more ignition advance it needs so if your CDI is not advancing then this would indeed affect power and ability to reach full revs.

  7. #6
    Banned qwerty's Avatar
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    How did the bike run before you rebuilt the engine? CDI boxes generally don't go bad because of a top end overhaul.



    What does "FL" mean?



    44 wheel sprocket is a mistake if you want top end speed. I'm not surprised an engine with a top end overhaul wont pull it. A stock engine will barely pull 50 teeth on a level road without wind or a cage to draft. I don't think a real "jedi mechanic" would approve of such a change, especially on fresh engine internals.




  8. #7
    Senior Member heyduke's Avatar
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    Does the bike rev past 50 when the back wheel is raised off the ground? If not I'd suspect the cdi. If it does then your just geared to high.

  9. #8
    Senior Member Henrici's Avatar
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    I had a 47 tooth on mine and when I put on the new chain I replaced it with a 45T. There is a pretty noticeable difference between the two. It also has to do with the heavier o-ring chain I imagine. That being said I drive from sea-level to 1500ft everyday and going up I average 45-50mph (verified by angry radar speed signs) but even when it flattens out the bike takes long time time to build speed.



    I can't imagine it would take much of a power loss to make going past 50 difficult with the 44T. With a that small of a sprocket are you shifting into 5th at 50mph? I usually shift to 5th at 40-45mph and I'm conservative on revving the engine.

  10. #9
    Senior Member greendub's Avatar
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    Quote Originally Posted by Henrici View Post
    I had a 47 tooth on mine and when I put on the new chain I replaced it with a 45T. There is a pretty noticeable difference between the two. It also has to do with the heavier o-ring chain I imagine. That being said I drive from sea-level to 1500ft everyday and going up I average 45-50mph (verified by angry radar speed signs) but even when it flattens out the bike takes long time time to build speed.



    I can't imagine it would take much of a power loss to make going past 50 difficult with the 44T. With a that small of a sprocket are you shifting into 5th at 50mph? I usually shift to 5th at 40-45mph and I'm conservative on revving the engine.
    It is your cdi. Just diagnosed this on another tw. ran with brown disconnected just like your bike. Plugged brown in and working cdi ran like new.

  11. #10
    Senior Member Camelrider's Avatar
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    My 1996 TW developed a similar problem. A few months ago it was running fine with 15/47 sprockets. It came standard with 14/45 sprockets and I have done some 40 000 km with them, the gearing was never a problem, even riding two up in the mountains. One day it started holding back and then pulling stronger again, until it stopped all together with pulling strong. Top speed wend down from 100 km/h to 75 km/h, that is about 50 MPH. I also tried it out with 15/52 sprockets and it was still under powered.

    Not connected with this problem, I was just about to take the engine apart to change the cylinder and piston to the XT225 cylinder and piston. While I had the engine apart, I also changed the timing chain. So far the TW had 80 000 km or 50k miles on its speedo.

    In the first place I suspected the carburetor to be clogged somewhere and that could be the cause of the bad performance. After taking the carb apart, cleaning it and changing some parts, I expected to have solved the problem.

    With this almost new and a little bigger engine I hoped for a little more umph. But the old problem is still there, uphill 70 km/h, on level ground 80 km/h, downhill it picks up some more speed. But downhill it will go without an engine also. It takes a long time to build up speed on level ground and it uses a lot of fuel. When opening up the throttle, the engine will at some point stop to respond/ developing more speed. From ¾ till full throttle there is no difference in speed, it may even go slower.

    Now I am checking the ignition, maybe the CDI is out of order. As I understand it, the CDI is responsible for the correct timing and advancing of the ignition. I suppose that the carb is good now with all the attention it got, so the only thing left is the ignition.

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