Engine Trouble WOT miss

Discussion in '2-Stroke Engines' started by OCCStingray, Apr 1, 2014.

  1. OCCStingray

    OCCStingray Member

    Just sorting out this bike I have now, it was running rough all thru the range including at WOT, to the point where you back ooff a touch and the power comes back. I replaced the sheet metal inlet manifold that was floating around in the breeze with a cast alloy one and cleaned out the carby and filter. The bike responds well now off the mark and anywhere on the throttle now with much less vibration but hold the throttle open and it does not like it one bit, seems lean to me (plug looks fine) so can I assume the main jet is clear and not too small? I am hearing alot about ignition advance damaging engines but surly that damage is a result of riding at WOT? I can not hold the throttle open due to lack of power and the horrible noise and vibration, back off a smidgen and the power is restored. Could it be crank case seals if all else seems ok?
     

  2. jaguar

    jaguar Well-Known Member

    lean running can be caused by seals, base gasket leak, intake leak, too lean jetting, pin hole in the cases (ie: chain wearing through).
    the noise and vibration are two other problems
     
  3. OCCStingray

    OCCStingray Member

    Noise and vibration are proportional to running condition. Would it be a safe bet that the main jet is not blocked if the carb performs well at all other speeds? NT Speed carby. NGK B6HS plug. Standard ignition. I'm assuming the main jet is the right size seeing the bike has some vintage. What's the easiest way to measure the main jet, buy a set of small hobby drill bits?
     
  4. jaguar

    jaguar Well-Known Member

    the main jet can have some fuel filter hairs partially blocking it and you can't tell any difference except at high rpm

    yes, a micro drill bit set
     
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