I need help with my throttle, possibly carb.

Discussion in '2-Stroke Engines' started by dzdaz, Feb 16, 2007.

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  1. dzdaz

    dzdaz Guest

    I just installed a 70cc engine on my bike and it was running great except for the throttle isn't working right. I unscrewed the cap where the cylinder and needle go in, pulled them out of the carb, then twisted the handle and it snapped back properly. The problem I seem to be having is everytime I put the brass cylinder with the needle back down into the carb then twist the throttle handle it doesn't snap back. The brass cylinder gets stuck at all the way open. Can anyone help me figure this out? How far down into the carb are the needle and cylinder supposed to go when you install them? I'm assuming they are supposed to slide up and down rather freely when using the throttle. Is that cylinder supposed to snap back down when when I let off the throttle? What am I doing wrong?

  2. Blaze

    Blaze Guest

    Can you take some photos?

    I had an engine that did the same thing. It was because the part that the brass cylinder slides inside of wasn't perfectly round. I took some pliers and gently squeezed it to make it perfectly round. Without anything hooked up, try sliding the brass cylinder in and out of the tube it goes into. If it sticks, you might have to adjust the tube to round it out a little better.

    Also, remember that when the carb goes back together, the washer with the slot in it goes ON TOP of the E-clip on the throttle needle.

    If that's not it, take some photos and it might help.
  3. gone_fishin

    gone_fishin Guest

    there's a little slot down the side of the slide, look inside the carb-cylinder, there's a tiny brass knob sticking out, the slot should be lined up with it. when you have it right, the "large" angled notch should be lined up with the idle screw.

    was that any help?
  4. chieflets

    chieflets Guest

    yup make sure u slide ur barrel properly wit the notch in the cyclinder if not you may have also damaged it on your barrel should be slit

    also some times i have found that unscrewing the barrel cap half turn does the trick too

    Chieflets :grin:
  5. dzdaz

    dzdaz Guest

    Thanks everybody. I think blaze has the right answer. dax also suggested sanding the cylinder down a little.
  6. dzdaz

    dzdaz Guest

    It was the slide getting stuck. I sanded down the cylinder a little and it's working great. My engine is stalling when I pull the clutch in now tho. It won't stay running. I also noticed that the engine hardly begins to pick up until I get about the throttle about half way open. Is this just an idle adjustment issue? And can anyone explain the choke lever on the airbox?
  7. Blaze

    Blaze Guest

    You may need to adjust your idle a little higher. You do this by adjusting the idle screw on the left side of the carb. Screw it in to increase your idle speed, screw it out to make it idle slower.

    Don't expect it to idle perfectly before it's broken in. You may have to set your idle a little high just to keep it running.

    As for the choke, the lever should only be moved up when you are trying to start a cold engine. As soon as you get it started you should be able to move the lever back down. Your bike might still run a little weak for a minute or two while it warms up.

    One of my motors had a problem with the choke vibrating into the up/on position, which made it run rough. I solved this by getting a spring from a hardware store and running it from the choke lever to a screw on the carb. Make sure to use a very thin, weak spring- one that barely has any pull at all. That way your choke lever should be able to stay up against the weak force of the spring, but when you get your bike started and you move the choke lever down, the spring will not let the lever vibrate back into the up positition.
  8. Blaze

    Blaze Guest

    Here is a picture of my choke spring installation. Note that the spring is made from very fine, weak wire. It works great.


  9. dzdaz

    dzdaz Guest


    Thanks for the insight guys.
  10. azbill

    azbill Active Member

    Dec 15, 2006
    Likes Received:
    grit ?

    the barrel of my new throttle was so tight I had to gently pry it out today :( Can someone tell me what grit I should use to smooth it up with ? I have some 1500 but suspect that would just polish it or is that the idea ?
  11. gone_fishin

    gone_fishin Guest

    a lil polishing might be all that's called for...can you see any high spots on the slide that need work? also, i recall someone saying something about a slide being out of round, maybe that's it?
  12. Guest

    Guest Guest

    Re: grit ?

    Make a "tube" of 400-600 grit wet or dry (black stuff) and turn the slide a few times, clean it off, then check your fit. You don't want to remove any more material than you need to. If you do, it will suck air and cause the engine to run lean.

    When you put it back for running, use a drop of Marvel Mystery oil or 3-in-1 oil.

    Don't use pliers or anything metal on a slide.... :p
  13. dzdaz

    dzdaz Guest

    fixed it

    I got my trottle working good now. I sanded the handlebars, the inside of the plastic grip, and sanded the cylinder that slides up and down in the carb. It's working great now.
  14. impression

    impression Member

    Apr 30, 2008
    Likes Received:
    i have a similair problem, the throttle is stuck all teh way open and i don't know what to do
  15. Flapdoodle

    Flapdoodle Member

    Oct 26, 2008
    Likes Received:
    Maybe this is too obvious, but I had the same problem when my knee hit the throttle cable where it comes out of the hand grip. Straightening it by hand fixed it, but it did take a few minutes to figure what had happened. Of course this had to happen in rush-hour traffic.
  16. thescooterguy

    thescooterguy Member

    Aug 8, 2008
    Likes Received:
    check the brass pin in the carb cylinder . the barrel has a groove , the pin guides the barrel , sometimes that pin gets moved , Ive seen it pushed all the way in. and sometimes out to far . if its out too far it will cause your barrel to stick if its in too far your barrel will spin which could cause binding on the throttle cable , there is a hole on the outside of the carb that houses the pin most of the time . you can use your smallest Allen to put it where it needs to be . so the barrel rides smooth but still has the guide. my photobucket is down right now i have a picture if you want one , its behind the fuel shut off valve the pin goes all the way through .if you have to adjust it remove the fuel valve first . they break easy if you apply presure to it . and thats a new carb if you dont have a parts carb laying around.
    Last edited: Mar 4, 2009
  17. Mountainman

    Mountainman Active Member

    Jun 15, 2008
    Likes Received:
    seems to be a common problem with tight sliding action in the HT carbs
    some real fine emory paper -- is all that should be needed
    unless slide is bent
    or casting inside of carb is off

    ride the motor bike