got fuel, got spark, can hear it popping but no start

Discussion in '2-Stroke Engines' started by Yolandi, Oct 10, 2016.

  1. Yolandi

    Yolandi New Member

    so fitted one of the 2 stroke kits to my bike last week (completely stock set up) and the first night with some fiddling it did start and ran for hours, next day wouldnt start and been the same since, iv done all the usual checks and iv got fuel delivery, spark (NGK BP6L plug), at one point my magneto earth lead fell off but iv re soldered it on, also polished off the varnish on the back of the magneto for a better contact, one thing iv noticed is the spark is very dim, almost impossible to see in day light, iv gapped it down to .025
    thinking about it it hasnt run since the earth lead came off and i resoldered it but when your pedaling you can hear and feel the fuel popping each time it fires but as soon as you pull the clutch in it dies instantly
    iv ordered a new coil because it was cheap enough but it hasnt arrived yet also measures the magneto volts and its giving out a max of around 6v

    i cant think of anything else to explore, help?
    also have tried a small amount of e-z start but no difference
     

  2. crassius

    crassius Well-Known Member

    several months ago, there were some mags that measured 480ohms instead of the usual 350ohms - at that time some CDI units would burn out one leg of their rectifiers giving them very weak sparks at low revs - if your mag reads that high, you may need a new CDI

    more likely is just a head gasket leak which is very common on these motors (look for oil seepage around head)
     
  3. Yolandi

    Yolandi New Member

    its hard to see seepage because i got the black coloured style but it is slightly wet on the fins around the gasket
    iv checked the mag and cdi and they were both within range ohm wise
     
  4. KCvale

    KCvale Motorized Bicycle Vendor

    Have you pulled your head?
    If so, did you re-install it with torque wrench?
    I torque my 66cc heads down to 20#, 5# at a time in an X pattern.
     
  5. crassius

    crassius Well-Known Member

    on black motors, I use a paper towel wrapped around an old hacksaw blade to check for seepage around head - clean it well with towel then see if it returns after a few tries to start it
     
  6. Yolandi

    Yolandi New Member

    yes i pulled the head just to see if there was anything obvious inside, i turned the gasket 90 degrees when i refitted adn yes tightened down with a torque wrench, just pulled the exhaust and lots of black fuel poured out of it when i turned it upside down but it can be blown through easily, wondered if it was choked up and blocked
     
  7. jaguar

    jaguar Well-Known Member

    6 volts? should be 30.
     
  8. wagel

    wagel New Member

    Had the same crap. First day running great, second day wouldn't even start. Spark was really weak and I could barely feel it if I stuck my finger in the cap and pushed the bike. It was a bad CDI in my case.
     
  9. Yolandi

    Yolandi New Member

    sorry was peak voltage at 29 (so probably 30) on AC meter, had it on DC when i took the 6v reading

    havnt really got the guts to stick my finger in the cap after working on some high voltage russian jeep engines XD
     
  10. jaguar

    jaguar Well-Known Member

  11. Yolandi

    Yolandi New Member

    What colour was your spark with a bad cdi? Mines currently light yellow and hardly visible, when the cdi was new it was bright blue
     
  12. KCvale

    KCvale Motorized Bicycle Vendor

    Just replace your plug with an NGK 5944 (BRR7HIX) Iridium spark plug and forget about it, it even comes pre-gaped.
    Best $10 you'll spend on your bike.
     
  13. Yolandi

    Yolandi New Member

    update, its not sparking with the plug installed only when its out and touching the head bolts, get the same noise with the plug lead attached and not attached
     
  14. crassius

    crassius Well-Known Member

    is the plug wet?
    if not, then you have a fuel problem

    did you try putting a few drops of fuel into plug hole then seeing if it will try to start?
     
  15. Yolandi

    Yolandi New Member

    plug is wet, tried a little fuel in the plug hole and a little squirt of easy start
     
  16. crassius

    crassius Well-Known Member

    I'd try a new plug, then try a new CDI if I couldn't check the timing - all those OK, I'd check compression
     
  17. Yolandi

    Yolandi New Member

    tried a new ngk plug, new CDI should arrive tomorrow or the next day, if that doesnt work ill see if anyone nearby has a compression tester or ill have to buy one, ordered a head gasket as well just incase
     
  18. crassius

    crassius Well-Known Member

    yeah, lots of folks carry a CDI & plug in their toolbag
     
  19. wagel

    wagel New Member

    I'm not sure I saw any spark at all in daylight and in dark garage I saw some yellow hint of a spark when rotating from pedals at high speed with back wheel in the air. When I stuck my finger in the cap I felt it was off. It is supposed to zap you so hard that you don't need to try a second time but mine was so weak that I could enjoy the tingling all day long:D. Don't try this at home.
     
  20. KCvale

    KCvale Motorized Bicycle Vendor

    You could have a big puddle of fuel in your crank case, seen it often in cases like this.
    Pull your plug, turn the gas off, then pedal up and down the street to blow whatever is in there out the plug hole.
    It's easy with no compression.
     
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