Engine lurching, anyone know why?

Discussion in '2-Stroke Engines' started by enriquez, Nov 4, 2007.

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  1. enriquez

    enriquez Guest

    Hey everyone,

    I'm still breaking in my engine, probably about 35 miles or so on it now. I'm finding that at about half throttle the engine wants to cut out. It sounds/seems like the engine is flooding when I try to give it more gas. I adjusted my carb e-clip to the highest position to try and lean out the mix, I live right about at sea level here in San Diego. Could it be just a break in problem? A spark plug problem? A air/fuel mix problem? I'm somewhat new to engine troubleshooting/maintenance.

    This problem happens with the choke off, and mostly when it's warming up. I haven't pulled to plug to see what color it is, I imagine this will give some more info. Any info is greatly appreciated, thanks,


  2. tfhudson

    tfhudson Guest

    Hi Scott,

    What kind of engine are you running? I had this same problem with my 70cc 2-stroke, and it was the choke lever vibrating upward as I rode, suffocating the engine. Next time it does it, check the choke.

    If that's the prob, take your carb off, remove the face from the intake and find the screw that holds the choke lever in place. Degrease the screw and its hole, put some locktite or fingernail polish or something on the screw and tighten it to where the choke lever is stiff to move. That should hold it for a good while, but get used to regularly checking tightening/locktiting/glueing-in-place most of the bolts on your bike, as the engine vibrations tend to make everything separate.

  3. enriquez

    enriquez Guest

    tfhudon, thanks for the help. I have a chinese 80cc 2 stroke, forgot to mention that... I have noticed that the choke will vibrate up while I'm riding. I'll definitely do what you suggested. Though, I have checked the choke while this problem is happening to make sure the choke isn't up. The engine still has this loss of power/flooding sound and feeling with the choke off.

    I'll try tightening the choke lever fastener as well as a new spark plug.

    Last edited by a moderator: Nov 4, 2007
  4. tfhudson

    tfhudson Guest

    Hi Scott,

    From what I've read, my 70cc and your 80cc are likely the same engine. I definitely had the same problem more than once early on, and on different occasions, the cause was different:

    My (uneducated) guess is that your spark plug is probably okay this early on in your engine's life, (but it wouldn't hurt to take it out and have a look at it.)

    Next time the problem starts, press down on the top of the spark plug boot with one hand while you're riding. See if that fixes it.

    If so, check the inside of the spark boot. If your boot is like mine (hard plastic), there's a little brass cap and pin inside that snaps onto the top of your plug, and behind that brass cap, there (should be) a small spring. Engine vibrations can cause all that stuff to come loose.

    My solution was to 1.) just remove the brass cap and spring and throw them away 2.) find a smaller diameter spring that I twisted onto the top of the spark plug, at its threads. Get one small enough so that you have to use pliers to twist it on, so it won't vibrate off. Let it stick up a few coils above the plug. 3.) Drill four small holes at the bottom of the plastic boot, and thread a small zip tie through those holes. 4.) Jam the spark plug boot all the way down on the plug and spring, so that the zip tie, pulled tight, grips hard against the outer ceramic ridges of the plug. This fix holds really firm for me!

    I also once had a spark plug wire that cracked and broke incrementally, right at the joint with the CDI box, so that in the process, it caused engine lurching. Replace that spark plug wire with an automotive one to be safe (see the thread here about accidental performance gains).

    Good luck!
    Last edited by a moderator: Nov 5, 2007
  5. atcspaul

    atcspaul Guest

    mine was also and it was because sprocket was not centered perfect. if you have the 5 hole sprocket they are next to imposible to center and you will feel it when you get to speed by a lunging feeling. the 9 hole is worth investing and changeing to
  6. Plug

    Have you taken your plug out yet to see what colour it is?
  7. atcspaul

    atcspaul Guest

    the new sprocket did the trick for me. all lunging was gone
  8. Skyliner70cc

    Skyliner70cc Active Member

    Mine cut out on me abruptly but mostly at full throttle. The vibration was causing the throttle kill switch to engage.
  9. dave1490

    dave1490 Guest

    i had this problem and it caused the pressure plate holes to elongate.the surgeing is still thier but it,s not transferd to the driver now.it fixed itself.lol
  10. Herrmanator8

    Herrmanator8 Guest

    Maybe there could be a possible bad connection between the wires from the magneto the the CDI case? maybe your missing a gasket causing a lean mixture? these are just some possibilities, check for these.

  11. Scottm

    Scottm Guest

    Hmmm. Did this issue get solved? When I had slack in my chain, the bike felt like someone was bumping me from behind every 5 -10 seconds. Plus check all the head bolts and the gaskets for air leaks.