Idling problem

Discussion in 'Bicycle Repair' started by Matzat, Aug 24, 2014.

  1. Matzat

    Matzat New Member

    I have been having trouble with my clutch lately. Whenever I try to go into idle, it races and almost jolts me forward. I have added in an 'o-ring' into the carb and the problem persists. ideas?

  2. LR Jerry

    LR Jerry Well-Known Member

    It would help to know what kind of clutch you have centrifugal or manual?
  3. butre

    butre Well-Known Member

    if it's a China girl, check more for vacuum leaks. if you don't find anything it may be a stuck needle
  4. jaguar

    jaguar Well-Known Member

    yeah, either the carb slide is not lowering enough when you let off the throttle or you have an air leak (which can also be at the crank seals)
  5. piecepatrol99

    piecepatrol99 Member

    Hi. My name is Ryan.
    I'm having an idle issue with my 49cc chinese motor. I've. Added a dual boost bottle kit (and yes it made a differnce) but now my mix is lean and I'm not sure how to correct it...
    The following factors are in play:
    The inner diameter of the intake manifold is 1/4" narrower than the stock manifold.
    I've adjusted the C clip on the carb needle but its still either idling high or stalling when the clutch is pulled in.
    Bottom end torque/power has increased, but top end is falling flat.

    What do you think the problem might be?

    I'm trying to avoid drilling out the new manifold or drilling and tapping the old one. (Once you drill it, you can't put it back).
    I've ordered a jet kit with 5 sizes of main jets for my NT carb. Should I go smaller or bigger on the main jet and/or get happy with the drill on the manifolds? IMG_20140722_140842.jpg

    I'm working with a very limited budget and I'm under the gun in time...
    Any helpful info would be greatly appreciated :)
  6. SOMF

    SOMF New Member

    For a quick check of vacuum leaks spray any suspect areas with carb cleaner, if the engine revs you have a leak. Use care around the carb to be sure cleaner isn't being sucked in through the filter or you will get a false reading. Also check your head gasket, a slight leak here will let your motor run but lean.
    piecepatrol99 likes this.
  7. piecepatrol99

    piecepatrol99 Member

    Thanks for the advice. I've already sealed the head gasket and haven't found any other leaks.
    A strange thing happend the other day... the end cap came lose on my muffler. When I stopped because it was suddenly loud, the motor purred like a kitten vs roaring like a lion.
    I think my next move will be a custom exhaust to match the boost bottles on the intake.
    I think I need to drill out the tail pipe and install a larger diameter pipe to relieve some of the back pressure. I also found a video on youtube that showed stuffing the muffler housing with 'fluffed' steel wool( without soap) helped to quiet the exhaust with out drasticaly increasing back pressure. As he was working on a 600cc four wheeler, I have some trial and error ahead of me... but I'll get her done ;-)

    I'll keep the carb cleaner in mind for future idle issue test.
  8. piecepatrol99

    piecepatrol99 Member

    I finally found the leak. Head is glued tightt. Fittings around boost bottle NPT fittings have been sealed with teflon tape and 2 part clay epoxy...and still had an idle issue.

    Then I noticed the throttle cable nut was always loose. Nothing major, just a quarter to a half turn. I put a flat O ring in it.
    Idle is now 1000 - 1200rpm instead of 2000 - 2500 to keep it from stalling when ever I had to stop.

    Thank you SOMF for pointing me in the right direction. All the hickkups I've had with motors in general before, intake leak was never one of them. I would have never thought...

    I also drilled out the tail pipe in the muffler end cap before I put the O ring on the throttle cable. That help to bring the idle down and increase bottom end power.
    I suspect that due to the lack of valves to close the combustion chamber, the exessive exhaust back pressure was making the motor stall for too much spent fuel in the chamber.

    Thanks again.

    Keep it between the ditches ;-)
  9. SOMF

    SOMF New Member

    That's great! They sure run good when all is right. I have been having a lean issue lately and it turned out to be a very slight imperfection in the head. I put it on a piece of glass with wet and dry sand paper and "trued" it up. Now no more lean issues.
  10. piecepatrol99

    piecepatrol99 Member

    When we first started chatting about idling issues and intake/head leaks, I did find a leak in my head gasket. The nuts were a little loose.
    While putting the wrench to it, I pulled the head off and applied a 1-2mm thick bead of silicone to the body and let it tack before reinstalling the gasket and head.
    Object was/is to seal the head without sanding. If it was leaking due to an imperfection, it isn't any more ;-)

    On a slightly different topic: my fork broke last week. The profile pic I have is no longer my motorized bike :-(
    I now have a 700c road bike instead of the 26" cruiser.
    Still using the same handle bar, stem and motor. Only thing I truly miss is my wide spring loaded seat.
    A great ride even though the tires are half as wide.
    Its a flip flop fixie. I've lost my hill climb ability (with out my 7 speed hub) and some off the top end. Thankfully its mostly flat for my commute to work. Just have to leave a little earlier and pay attention not to beat the motor too hard. I did just get it running right after all...

    Next is a 3 speed cassette to replace the single cog freewheel and a larger chainring on the front freewheel/pedal crank. I'll have my hill climb ability and top end back...

    Loving my jackshaft kit! ;-)
  11. piecepatrol99

    piecepatrol99 Member

    Where did you put the O ring? I found my leak at the throttle cable lock nut.
    I originally placed an O ring in the carb where it connects to the manifold. Turns out the 'draft' wasn't at the front door, but in the roof...
    Placing the O ring on the throttle cable solved idling issues for me.