Messages

1

Vintage Two Strokes / Rebuild of '80 YZ250G all but done but .... BUMMER ! Bike runs bad... ignition.

« on: June 23, 2013, 04:58:45 AM »

I need help from guys with YZ experience or at least CDI ignition knowledge. Bikes now all but done upon starting it won't rev past maybe midrange, just blubbers/ breaks-up sounding "sorta" like it s rich... but it's not. Absolutely not a carburation issue... though I did replace parts in there, floats, fuel inlet needle and seat, 370 main jet.( other stuff in there is stock sizes and look good.)
  I bought bike knowing P/O claimed ignition problem... he's right.
    Things ruled out:
   -Kill button is off ,not an issue.
 - I've tried 3 different high tension coils and it runs same. Plus, the original coil tests ok anyway.(Pri. winding= .6 ohm. Sec. winding =5.8K ohm. Plug cap and wire insulation looks good.
  -I bought a USED Ebay  CDI box. Came from a running 80 or 81 250.... so the seller claimed. No tests specs for CDI box I know of. .... IS THAT CORRECT ?
  - both coils on stator plate check out resistance ,  one is .6 ohms, other is 1450 ohms. Well within specs. They also LOOK like new.
  - Rotor feels to have strong magnetivity....any ferrus metal sticks like hell to it.

 So, is running symptom indicative to still having a bad CDI box? I HATE to buy another ebay used one but whats a guy to do ! !

  help ! !   And thanks. dave

2

Technical / 1980 YZ250 ignition timing.

« on: April 30, 2013, 01:35:32 AM »

It is a  Hitachi ignition, an internal "button" rotor. ('80 YZ250).
     Playing around with different possibilities looking for clues to what's possibly right.... when I set piston @ TDC and then line up dashmarks on rotor and stator there happens to be a punched dot mark on the stator plates O.D. that also lines up with a edge of the engine case. This might be some P/O's attempt to mark where stator goes,( or it might be a factory punch , I dunno).

Any 1980-'81 YZ owners out there that are familiar with Yamaha's marking methods? dave

3

Technical / 1980 YZ250 ignition timing.

« on: April 28, 2013, 05:37:38 AM »

 Finishing up my rebuild of this vintage bike, I realized I'm a little stuck on ignition advance setting. Unlike an RM, the YZ has no match marks between  the O.D. of the stator plate and the engine case. Instead the yz  ROTOR has a dash mark as does the ID of the stator plate  . Obviously they are to line up at some piston position. Hoping some old YZ owners might just be able to give me the spec and procedure. Are the hashmarks to line up at TDC or a "x" demention BTDC ?  No guessing here please .... only out of your manual or your experienced brain.

Thanks much guys, dave