Plug Chop Help Request for the Experts

Discussion in '2-Stroke Engines' started by flashstar, Sep 17, 2013.

  1. flashstar

    flashstar Member

    Hey Motoredbikes members,

    I have been working to tune my GT50R thatsdax engine. I reduced the compression ratio to roughly 9:1 then installed a fiberglass reed valve. The engine runs very well with the thatsdax RT carburetor but a size 75 jet is so large that the engine sputters and died after 5 minutes. An examination of the CR5HSB NGK plug revealed that the tip was black and wet.

    I installed a size 70 jet (the next size down), installed a new CR5HSB plug, and rode around the neighborhood quickly. I put about 4.5 miles on the bike and made a couple of near full-throttle runs. The engine ran very well and pulled like hell up all hills. Then I shut off the engine and checked the plug again.


    If this were from my car, I would be very happy. I'm concerned though that I'm running a bit too lean. I just ordered in a cooler CR6HIX iridium NGK plug to replace this hot, cheap copper plug. Do you think that I will be safe with the new 6 series cooler plug or should I try to increase the jet size a bit? The jets only come in intervals of 5 so I would need to carefully drill out the center.


  2. Fabian

    Fabian Well-Known Member

    That plug looks like it's been run in a very lean air/fuel ratio, considering it's come out of a 2-stroke engine.
  3. IbedaYank

    IbedaYank Member