Idle fluctuating up and down

Jsbowling42

New Member
Jun 19, 2020
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Hello, I recently noticed that my idle is going high(slightly) and then lower, what I would call a hunting idle. I have a NT China carb and the 66cc engine is stock. My first thought was an air leak but then thought that an air leak would cause only high idle is this true? I took off the air filter to look at the slide as this was happening to see if there was any movement but there wasn’t so I could rule out the throttle cable I think. I was able to stall the motor with carb spray around the exhaust side of the base cylinder gasket but it’s so close to the case gasket I don’t know which it could be. Any ideas on where to go from here would be great thanks.
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
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Try soap spray in the same area. It won't hurt the engine, and should show you a little more as to where the leak is.
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
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It would be easy to GENTLY tighten the head/jug bolts, and/or replace the base gasket. The case gasket isn't that hard, just more of a disassembly/reassembly hassle.
 

Jsbowling42

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Jun 19, 2020
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Thanks I’ll try that in a bit and report back. Have you ever see an idle fluctuate up and down from an air leak? I would think it would just stay high.
 

Jsbowling42

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Jun 19, 2020
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Hmm.. well I’ll try the soapy water and fix the leak and go from there. One step at a time. Ha I’ll let you know how it goes.
 

Jsbowling42

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Jun 19, 2020
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Well I did the soapy water trick. Didn’t see any bubbles. Though the idle was fine when I started it up.
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
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Ohhhh been awhile. I believe you set the float to be even with the carb body when it just touches the valve. I meant to check for debris in the seat or other reason it would intermittently interrupt fuel flow.
 

Jsbowling42

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Jun 19, 2020
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So if your interested. I found the air leak, it was the seal behind the magneto. I guess it had vibrated it out. Carburetor cleaner made the engine die because it ran down into the magneto housing ha. I guess the soapy mixture Didn’t make it past the magneto housing gasket not really sure. But when I took the magneto housing cover off I felt the puff puff Like it was the end of an exhaust pipe lol
 
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