will damaged throttle cable cause air leak?

Discussion in '2 Stroke Bicycle Engines & Kits' started by sboricic123, May 20, 2017.

  1. sboricic123

    sboricic123 Member

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    Hey folks, I have a 66cc Grubee, NT carb that came with the kit. I ran it all last year plus about 5 trips so far this year.
    I was out for a ride and all of a sudden lost power and the engine won't even idle now but still starts up. I replaced fuel filter, lines, fresh gas (40:1), spark plug, tried a new muffler, magneto and checked for air leaks on cylinder head, intake and crankcase seal.
    I do have a damaged throttle cable where it connects to the carb. Will this cause air leaks and might be the problem?
     
  2. sboricic123

    sboricic123 Member

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    I should add, I cleaned the carb and also tried another 1 I have kicking around.
     
  3. MEASURE TWICE

    MEASURE TWICE Active Member

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    I remember someone saying how they check for air leaks by spraying a little WD40 around the suspected leak area while the engine is running to see if there is a change in engine speed. If it changes then it indicates a leak as you have to figure that the WD40 is stopping at least some of the air leak if not all. It is not a normal running with extra stuff like WD40 spray in the fuel air mix, but that is not the point. It is only to find a leak.

    Tom & Ray as Click & Clack on Car Talk Radio had mentioned at their garage they used propane. Also stethoscope in some way to listed for what sucks... haha! Rest in peace Tom.
     
  4. crassius

    crassius Well-Known Member

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    what is "engine won't even idle now but still starts up"?
    what is "damaged throttle cable where it connects to the carb"?
     
  5. 2door

    2door Moderator
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    To answer your question; No. You could remove the throttle cable and still not cause an air leak. This is a common misconception with the NT carburetor. Some will advocate sealing the cap where the cable attaches to the carb body. It is unnecessary because the throttle barrel, or slide, does the job of 'sealing; that area. An air leak would have to occur below the throttle barrel and downstream of the carburetor.

    The most common places to find a leak will be where the carb attaches to the intake manifold or where the manifold attaches to the cylinder.

    You'll also want to avoid over tightening the cap where the throttle cable goes. It has been proven that doing so can warp the carb body enough to interfere with free movement of the throttle barrel (slide). Finger tight is sufficient.

    Tom
     
  6. sboricic123

    sboricic123 Member

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    Crassius, it's just the plastic housing around the cable that is damaged. I should have been more clear. I can get the engine to start up, but it won't stay idling if I adjust the carburetor idle screw. I'm lost as to what might be causing the issue. It revs up but not like it should. That's without me on it. When I do try and take it for a ride, it barely moves and dies when I engaged the clutch.

    Tom, thanks for your input too.

    I tried the WD40 trick for air leaks while I had it running and holding the throttle a bit, but didn't notice any difference in rpms.

    I'll just go over things I have tried with no success:
    -fresh gas (40:1)
    -new gas filter and hoses
    -tried a new exhaust
    -changed magneto but not the magnet itself
    -new spark plug
    -checked for air leaks around cylinder, crank case and intake
    -new CDI
    -tried a different carburetor
    -cleaned air filter
    -made sure cylinder head bolts were torqued to 12 psi
    -check intake bolts that they were tight
     
  7. crassius

    crassius Well-Known Member

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    a compression test usually can tell you if a seal is blown - many auto parts stores will loan a tester
     
  8. sboricic123

    sboricic123 Member

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    I decided to go ahead and try and change the crank seals. I was able to get the one out easily by the magneto. But the one behind the drive sprocket is coming off in pieces. Is there an easy solution to get all the pieces out or just pick away at it?

    I think I found my answer. I had another engine that had a different type of seal on it.
     
    #8 sboricic123, May 21, 2017
    Last edited: May 21, 2017
    Dan likes this.
  9. Tony01

    Tony01 Member

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    12psi torque?

    You can check for leaks by holding an unlit map torch around with the gas coming out, very close at all the seal points.

    Use two gaskets at your intake flange. Make sure the flange is flat like a skinny girls chest. Use a file or sandpaper on granite to flatten.

    Also 40:1 is too little oil, try 30:1

    Could also be your timing, if it's retarded then your motor will run retarded
     

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