Throttle is wide open and I can't control it

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Marcey

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Jul 14, 2013
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Hello, i just bought a used 66cc motor bike off of a guy and when running the engine constantly runs wide open at full speed and i can't control it otherwise. My throttle cable and grip assembly were mangled so i replaced those and it still does the same thing. I spent all day trying to adjust the screw where the cable sheath goes into the screw on top of the carburetor and on the grip side because it seems to not fit very well. It runs fine I just can't control it no matter what way i twist. Any help is greatly appreciated.
 

bairdco

a guy who makes cool bikes
Aug 18, 2009
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check the slide on the carb and make sure it's in correctly. it's the grey round thing with the brass needle in it. it has a slot that lines up with a tiny pin in the carb body. if it's not lined up so it moves freely it jams.
 

Marcey

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Jul 14, 2013
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Hey thanks for responding. The tube with the needle appears to be lined up with all the right studs inside the body of the carburetor. I tried putting it back together in slightly different variations and the problem is still the same. When I have the cap off and twist the throttle it pulls the assembly back and forth as logic would think that it should. So, I 'm pretty baffled. I went ahead and ordered a new carburetor for $11 just to see what will happen. In the mean time I've been using the kill switch as a way of slowing down, haha.
 

MotorBicycleRacing

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Jul 28, 2010
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What carburetor do you have on your motor?

If you have the NT carb it sounds like you have a large air leak where your carbs throat fits over the intake tube.
If you full choke your carb by pulling the lever all the way up does your motor die?

if it keeps running and only slows the rpms down a bit it indicates an air leak.

Get a O-ring to seal the end of the intake tube inside the carb throat.
Home Depot sells them in packs of 10 for $2
 

crassius

Well-Known Member
Sep 30, 2012
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I'm thinking that someone overtightened it at some point in its life and now the body of the carb is bent a bit & binding the slide - adding a 2nd spring can help, but your new carb will help more.
 

Marcey

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Jul 14, 2013
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Hey, thanks for all your help guys. I got the new carb and utlimatley had to take the some of the internals out of the new one and put them in the body of the old. But, everything works now and I became very apparent that the problem was that the tube that the throttle cable is attached to was stuck very high up in the body. But yeah, it all worked out, Thanks again.
 

mapbike

Well-Known Member
Mar 14, 2010
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Hey, thanks for all your help guys. I got the new carb and utlimatley had to take the some of the internals out of the new one and put them in the body of the old. But, everything works now and I became very apparent that the problem was that the tube that the throttle cable is attached to was stuck very high up in the body. But yeah, it all worked out, Thanks again.
Glad to hear you got the problem solved, always a good feeling to finally get things figured out and fixed.

Rubber side down and happy riding.
Peace, map
reddd