Engine Trouble How's this plug look?

Discussion in '2-Stroke Engines' started by four cu, Aug 23, 2014.

  1. four cu

    four cu New Member


    Plug chop. No leaks whatsoever

  2. four cu

    four cu New Member

    Only on 5th tank
  3. Fabian

    Fabian Well-Known Member

    I looks lean
  4. Fabian

    Fabian Well-Known Member

    This is what your spark plug should look like with the engine running at wide open throttle for long enough that the cylinder head temperature has had time to stabilise.

    The photo represents prolonged periods of wide open throttle between 3,500 and 3,800 rpm, using Australian (lower eastern states) 98 octane fuel and 25:1 oil/fuel ratio and a CR Machine Manufacturing low compression straight plug billet cylinder head and a Jaguar CDI using jumper settings selected for the most advanced ignition curve.
    I am running a No 77 jet in the NT carburettor with atmospheric conditions at the time being an 18 degree (65 degrees Fahrenheit) day with 59% humidity and approx 120 meters elevation above sea level.
    The cylinder head temperature was 140 degrees Celsius (266 degrees Fahrenheit) and the exhaust gas temperature (read from an onboard KOSO EGT sensor and gauge) was 370 degrees Celsius (700 degrees Fahrenheit).

  5. HeadSmess

    HeadSmess Well-Known Member

    fabian, you covered EVERY detail, bar one...

    what plug are you using?

    the heat range of a plug denotes how clean or dirty it will be. ngk 4 will be white, while ngk 13 will just be a hideous black mess, on the same settings...

    try it out one day ;) get the lowest and the highest b*hs you can find.

    and the difference in head temperatures will astound you :eek:
  6. Fabian

    Fabian Well-Known Member

    I use an NGK BP8HS

    In an air cooled application, it pays to use a reasonably cold plug to cover yourself against extremes of cylinder head temperature, especially when using the standard cylinder head which can make it's way past 300C* (572 Fahrenheit) on a hot day, particularly when climbing a steep gradient, with low air speed passing over the cylinder head.
  7. HeadSmess

    HeadSmess Well-Known Member

    ^^^ :iagree: cept i use a 6 usually... usually.
  8. Fabian

    Fabian Well-Known Member

    Nothing wrong with a No 6 heat range spark plug, though my experience with NGK has shown that you can get away with a No 8 heat range, thereby covering yourself for a wider range of cylinder head temperatures, minimising the chance of pre-ignition from an excessively hot electrode when cylinder head temps start to go stratospheric.
  9. HeadSmess

    HeadSmess Well-Known Member

    :iagree: didnt i post a thread that said something about if you do something silly like use a number as HOT as a 2? :)

    and as jaguar once tested... the hotter spark plugs also raise head temperatures, not by a few degrees...but by a LOT!