Engine Trouble Engine stalls instantly after a single pop noise

Discussion in '2-Stroke Engines' started by MarathonMan123, Apr 8, 2015.

  1. MarathonMan123

    MarathonMan123 New Member

    I just built my second motorbike so I have some experience with them but not a lot. So I just got My bike working and I'm taking it for a test drive and it starts, but when I pull down the throttle it bogs but very slowly picks up rpms but then it'll Make a single pop sound and then stall out instantly after it. I am able to start it up again but it will run for 15 seconds and then it'll do the same thing again. I've tried adjusting the choke from half open to completely open to closed but It will still do the same thing. This isn't the first test drive. But it's never done this before (I brought over the engine and its components from my first bike). I don't know what is causing it. There isn't any air leaks that I can tell since the first few test drives I fixed the air leaks with new gaskets. Nothing is blocking the gas from flowing to carb . the carb was cleaned before I installed it I have the gas and oil ratio 1:16. I checked the magneto and its still on tight. All the wires are connected properly no shorts anywhere. Could it be a timing issue, gas issue, electrical issue? I really don't know. Any help will be greatly appreciated. I'll send pics if needed

  2. Timbone

    Timbone Active Member

    I am no there but it sounds to me like...

    you are not getting proper fuel flow. Perhaps it is starting with a full float bowl, runs lean and then runs fast just as it runs out of fuel and dies instantly. I would double, triple and quadruple check your fuel line, making sure there is no obstruction or vapor lock.

    Good luck.
  3. dougsr.874

    dougsr.874 Active Member

    Make sure the gas oil mix is correct...I didn't clean out my container once and ended up with to much oil in the mix...had me baffled till I realized what I had done.....
  4. MarathonMan123

    MarathonMan123 New Member

    I've been using that mix forever since I got the kit a year ago and I've cleaned out the tank and the carb and I got new fuel line that the gas doesn't erode Never had any problems until my old Chinese cdi broke a. Few days before this problem. Occurred and it was working perfectly fine then, and I was riding it on steep hilly terrain. So I bought a new one and then that's when it started occurring. Could it be the new cdi? I bought a "better one" it was the, "Super Charge CDI for 48cc 66cc 80cc - High Performance" from GasBike.net
  5. crassius

    crassius Well-Known Member

    I've seen a bad CDI do this when an internal connection goes bad & throws off timing, but after that they usually won't start again. Worth trying another tho.
    MarathonMan123 likes this.
  6. dougsr.874

    dougsr.874 Active Member

    Your mistake was buying anything from Gasbike....Kings & Zone 8 are same company
  7. MarathonMan123

    MarathonMan123 New Member

    I'll try another cdi
  8. jaguar

    jaguar Well-Known Member

    you have a bad seal between the cylinder and head.
    plane both surfaces using glass and sandpaper and then make your own gasket from high temp gasket material.
  9. MarathonMan123

    MarathonMan123 New Member

    The next cdi didn't work. also how can it be the head gasket? When I pedal to start it up, since I have the shift kit, I feel it compressing how is it the head gasket if I never took off the head for any reason? I'll try it but before I do, I just want to understand how or why that is the problem because i don't want to cause more problems Than I already have with the darn thing.
    Last edited: Apr 9, 2015
  10. crassius

    crassius Well-Known Member

    I've never had to sand a head surface - a quick look should tell you if it is leaking there, but a lot of trying to start it should show some oil seepage anywhere a gasket is leaking.

    A popping noise is often associated with a crank seal failing, but then one usually gets just the one pop.
  11. MarathonMan123

    MarathonMan123 New Member

    There is no oil dripping out of the engine or splattering on my leg. I've had it spit on my leg but that was because of a bad exhaust gasket and I'll look because it wont hurt and because I'm out of of options. And also something I noticed is that my intake manifold isn't 30mm or 40 mm. It's somewhere in between. It's a pain in the butt because I have to make custom gaskets for it. Could it be an air leak that I didn't notice by the intake because of a faulty offset tube I had to modify?
    Last edited: Apr 10, 2015
  12. crassius

    crassius Well-Known Member

    I've never had an air leak that caused a popping sound, but it never hurts to check everything, then check it again.

    the 2 rules for these are

    1 - don't get lazy

    2 - don't get in a hurry

    just finished a customer bike today that wouldn't start

    tried 3 CDIs, tried 3 spark plugs, tested mag ohms reading, took nut off rotor & checked position, took carb apart & cleaned it, emptied gas tank & tried fresh fuel, took small bevel gear off to check seal, was about to take off rotor to check that seal when I finally noticed he had already taken the mag coil off once, & put it back on upside down so timing was off - turned it right side up, started the bike, the sat & swore for 'bout 1/2 an hour