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Discussion Starter #1 (Edited)
This thread replaces the CDI repair thread and please use it just for CDI questions and problems.

Starting almost a year ago I set out to make replacement CDI for TW200s after being asked to make them for BW200, exactly the same engine but with different pickup coil resistance. Since then R&D have taken most of the time, but now I have a replacement for 87 to 97, 98 to 00, and 01 on. These CDI have micro processor timing control, rev limit at 9K, tach output wire for a ground pulse tachometer like the low cost ones on Ebay. Available at https://cdiparts.com/Yamaha/yamaha.html in stock and ready to ship.
All BW200 CDIs are available exclusively at https://www.fattireconversions.com/bw200parts.html#electrical

Most people don't seem to understand CDIs or how they work. Yamaha complicates that with their pickup system. On TWs there is one pickup coil and a bar on the flywheel that is 60° long. The leading end of that bar passes the pickup and makes a negative pulse at 70° BTDC, the trailing end of the bar makes a positive pulse at 10° BTDC. The pulse at 10° fires the plug for starting and low rpm, but the 70° pulse must be inverted and then delayed based on rpm to fire at the correct time based on information in the micro processor.

Original TW CDIs used a crude RC time delay that was controlled by rpm. Effective but not extremely accurate.

Inside the flywheel is the magneto coils and charging coil. The high voltage coil outputs approx 150 volts which is rectified and used to charge a capacitor. That capacitor is then discharged across the primary of the ignition coil, a special low resistance coil used just on CDI ignition. Original TW CDIs also used a smaller coil or a tap on the HV coil to provide low voltage power to operate the CDI. My CDI takes the HV and with a special voltage regulator puts out 5v for the micro. The micro processor then looks at the rpm and knows what delay to use for each spark giving precise timing control.

Thanks for all the support, it has been a long journey but we are here.
Tom
 

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Should we expect any noticeable improvement in performance over the stock module, or is this just to be considered a more cost effective replacement in-case of a failure of the oem unit?

Thank you for all your hard work on this.
 

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Should we expect any noticeable improvement in performance over the stock module, or is this just to be considered a more cost effective replacement in-case of a failure of the oem unit?

Thank you for all your hard work on this.
My 87 was running mediocre with the stock cdi. Not great but running. It would cut out and die after about 20 min of running though and all signs said CDI...

I took a chance with Tom's product and I can say there is an improvement. And I believe the rev limiter has been raised or eliminated...?
 

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I applaud those with specific but technical abilities! I am personally pretty good with a wrench but I suck at electricity and all things electrical. I leave these issues to those who have the technical know how to tackle them. This is very easy to say, there is nothing that intricate about the CDIs in our bikes but I must preface that with "For those who have the technical abilities". Thumbs up to Tom for tackling this often problematic issue for us. The older members here will understand this well but QWERTY would be tossing all sorts of negativity toward Tom over this upgrade.

If it works then go for it and do report back to us, what do you have to lose when the CDI in your bike has already crapped out? On the 1987 TW in particular it makes no sense to buy and replace a faulty CDI with the exact same faulty CDI it originally had in it. There is always someone making a better mouse trap and it does stand to reason the parts available today should outshine those from 30 years ago if the guy putting them together knows his trade.

Best of luck Tom and thank you for your efforts.

GaryL
 

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Discussion Starter #8
Should we expect any noticeable improvement in performance over the stock module, or is this just to be considered a more cost effective replacement in-case of a failure of the oem unit?

Thank you for all your hard work on this.
The performance improvement is just that your TW will run like it was supposed to.
 

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Discussion Starter #9
Isn't the '87 cdi different than all the subsequent years?
The original CDI for 87 was different in the way it was powered by the magneto. Mine are all powered by the HV so all my CDIs are the same, just different wire harness.
 

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Discussion Starter #10
My 87 was running mediocre with the stock cdi. Not great but running. It would cut out and die after about 20 min of running though and all signs said CDI...

I took a chance with Tom's product and I can say there is an improvement. And I believe the rev limiter has been raised or eliminated...?
Rev limit is set at 9000. This is effectively the limit recommended by Yamaha.
 

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As a side note, I still have a disdain for the over-complicated carb.
The stock carb is very hard to tune compared to the Mikuni VM26-606. The VM is a race carb so you can change main jets in seconds without removing the carb from the bike. There is a removable bolt on the bottom of the float bowl that makes changing the main jet quick and easy. I'm not affiliated with this company but have bought two of these carbs for two different bikes one being my 1990 TW200. tboltusa.com part#TBW0399. The VM carb fit on my 1990 intake boot. It makes it easy to eliminate the airbox and use a foam or cone filter.
 
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