Frustrated .... '74 Yamaha TY250 Trials ran fine but a little flat at top end. Decided to try a CDI kit to get better performance. Installed the CDI kit and wouldn't start. I rechecked and set the timing with a strobe lite and turned the crank using a drill with socket in the CCW direction. Prior to timing, checked and marked TDC and .122" piston BTDC location on crank case. Next I pulled the spark plug. With the plug grounded to case i see a nice blue arc when i use the kick starter.  After kicking my leg tired. Pulled the plug and it was wet. I pulled the plug and let the cylinder air out overnight and tried the next morning. No start. the kill switch in not part of the wiring at this point. So that is not shorting the coil to ground, ie have a spark.

Since the bike ran before, I didn't think any thing like fuel quality or flow were an issue. But now having to go down that road to pull Carb and flush it clean and with fresh fuel. Do you guys see anything I might be missing. Been at this now for a week and no starting.....frustrated

Seems like you have done everything correctly.   Since you made the timing mark, are you sure it is BTDC and not ATDC?

As a general comment, digital CDIs need their pickup location well in advance of the firing point to allow time for computation.

It takes significantly higher voltage to fire the plug under compression than in open air.  Try reducing the plug gap to half what it is now.  I would not use the bike that way, just as a diagnostic test.

If still no success, I would refit the OE ignition to verify the bike runs.

Can you post a link to the Malaysia OHT bikes CDI?  I can't find it with a search.

I found this: https://www.ohtokc.com/products/electronic-ignition-yamaha-ty250-hit

Did not see any written installation instructions on that website.

Hi Konrad, I had a similar issue with my Ohtokc Ignition for my TY175.  It had spark, and would run, and after getting the timing set, put everything back together thinking it was fine, then I couldn't get it started for the life of me.  I thought the maybe the kill switch was faulty, maybe I didn't secure a wire, or pinched and shorted it, nothing made sense.  Pulled it all back apart, and couldn't find anything abnormal initially.....

I checked the solder points on the Ohtokc ignition coil, and both were cold joints, and the lower had separated completely.  I'm not sure if this may be your issue, but I ended up desoldering them completely, and redoing the connections. It's been great ever since.   Not saying this is your issue, but may want to double check the connections for the same problem.

There was a lot of other fiddling I had to do with my Ohtokc to get it to fit right, and work properly.  The price point is very tempting, but it definitely wasn't a straight forward install. 

(Imgur decided to dump all the photos again. ugh.)

Detail of where the cold joints were:

 

 

 

Wiring diagram I was sent after purchasing the kit. Again, TY175 specific, not sure if it will help you:

 

Edited May 27, 20251 yr by diagnosis
added images.