Engine Trouble Mind Boggling Issues--Unable to Start

Discussion in '2-Stroke Engines' started by robmac571, Sep 27, 2015.

  1. robmac571

    robmac571 New Member

    Hey guys,

    Having some issues staring up my friends bike that we started building three weeks ago. I've built 4 bikes in the past and have been riding them for around 4 years.
    One morning he was riding it back from class when it started to lose power and then completely died out. This was after 10 days of flawless riding with a 20:1 fuel ratio.

    Knowing this, I immediately checked for a loss in compression, but all of his head nuts were pretty dang tight and his head gasket was not blown. His compression was still great, so it couldn't be that.

    Next we checked his carburetor and cleaned it out twice, blowing some compressed air down the jet, and later mixing up a brand new batch of gas. That did absolutely nothing.

    After that, I took a look at his electrical system. I unplugged the kill switch and checked for a spark--which there was--and then checked all the connections inside the magneto just to be sure. We tested everything for their respective resistance values which all fell within the boundaries.

    At the moment, when he pedals heavily downhill with no choke, his engine fires every two seconds or so, not in quick succession like it should.

    So what could the problem be? I have a hunch it might have to do with the timing but I have no idea at this point. Any help and suggestions are greatly appreciated!!

    Jacob's Bike 1.jpg Jacob's Bike 2.jpg Jacob's Bike 3.jpg Jacob's Bike 4.jpg

  2. V 35

    V 35 Member

    Hunch ... Crankcase oil seal leak, that would still give cylinder compression, but would not allow fuel to be drawn in to ports .
    Test = Thick oil on seals, try engine, thick oil - seals for few moments .
  3. robmac571

    robmac571 New Member

    Okay thanks! I'll get right on that first thing tomorrow and report back.
  4. butre

    butre Well-Known Member

    could be not getting spark under compression
  5. robmac571

    robmac571 New Member

    So, just checked, and its definitely not the crank case seal. Can you describe what goes on when the plug cannot spark under pressure? How can that be resolved?
  6. butre

    butre Well-Known Member

    no spark under compression is weak magneto and the only way to diagnose is to replace with a known good unit or attach a multimeter, but I don't remember the values you're looking for for the multimeter.

    have you checked that the float isn't sticking or the exhaust isn't clogged? the exhausts with a catalytic converter get clogged very rapidly, especially with such a rich fuel ratio
  7. crassius

    crassius Well-Known Member

    we saw several CDI units go 'weak' a few months ago - they make a spark when the motor turns fast enough, but won't make a good enough spark at starting speeds - if you have another bike there, it is easy to swap it out for a quick test
  8. Fabian

    Fabian Well-Known Member

    I had mind boggling issues for a good 2 years with my bike, until i finally got it to be perfectly reliable.
  9. V 35

    V 35 Member

    Could be a cracked spark plug Could be a bad CDI box . Id have a spare [ preferably tested OK ] Spark Plug, Magneto Coil, CDI box
    This way, you can swap in known good parts. A spare carb is always smart too .
  10. HeadSmess

    HeadSmess Well-Known Member

    new plug, make sure it sparks when its RESTING ON THE HEAD. the head can sometimes be electrically isolated... bad.

    no muffler, no carb, just a plug and ignition...splashadash of fuel down the intake and if it STILL doesnt fire...?

    check the woodruff key in magneto/timing.

    try flipping blue and black around.

    if it did start it was the carb or the muffler.