What's the correct plug gap for LD Z4C?

Discussion in '2-Stroke Engines' started by Irish John, Apr 10, 2009.

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  1. Irish John

    Irish John Guest

    I'm having real problems getting a fairly new motor to fire up. I've replaced Magneto & CDI but I'm not sure of the correct plug gap for the standard kit plug. Can anyone tell me?
    I'll check it for a spark to see if it's working but this time I am really becooming flummoxed - never been hard to get these motors to fire up before.

  2. arceeguy

    arceeguy Active Member

    Out of the box, the stock plug gap is around .025-.030. I don't know what the specification is, if there is any.
  3. Irish John

    Irish John Guest

    I looked at the instructions which say 0.6 - 0.7mm
    I'm thinking it may be a carby problem now. The green wire and striped wire that come down from the kill switch go striped onto the white wire from the magneto and green earthed to frame. The blue & black wires that come out of the magneto go to the blue and black wires from the CDI. This might be wrong and might be causing the problem. It's so long since I worked on an HT that I forget but I never used to wire it that way - I think I connected the green & striped together into the white magneto and the blue & black to matching colours on the CDI.
    I know the answer is simple cos it always is.
    I'll check all that tomorrow and make sure the motors not flooded as well but if it was flooded it would cause hydro lock and I'd know and remedy it by removing the plug & exhaust and running downhill until it spat it all out.
  4. arceeguy

    arceeguy Active Member

    I think your wiring is correct. In this case, the white wire is being grounded to squelch the magneto output, killing the spark.

    An easy check that I do is to remove the spark plug and lay it on the head, then roll the bike back and forth in gear. You should see spark.

    Also check the gap between the stator coil and magnet. I shim the gap with credit card stock. I did have a "no start" condition on a brand new HT that was caused by too much of a gap between the stator and magnet. It was too wide, but once I tightened it up, it fired right up. I check every engine as part of a "pre-flight" routine. I guess for $100 USD, I can forgive some sloppiness in assembly. All in all they aren't any worse than a typical American car was in 1975.
  5. eisle89

    eisle89 Member

    I had the same problem as you I think I went all through the electrical side and the fuel side. Then as a last resort I thought maybe the clutch wasn't turning the engine over well enough, so I tightened the clutch plate about a 1/4 turn. And that did it, starts up on the first pop now. I did feel kinda embarrassed though. ;)
  6. wanger

    wanger Guest

    the best plug gag for a LD4 is remove it {now gaped from engine ]
    and insert NGK B#HS with good lead:idea: