Trouble dialing in air mix and idle

85CTrider

Member
i have a 1985 ct70 - new air filter , new spark plug, carb is fine etc..fuel flow good i am having a problem with the bike stalling while in first gear and sitting idle...the bike idles fine in neutral - but when in first gear will stall... i turn up idle and turn in air screw..... all good on idle - idles perfcet - the choke is very sensetive... if bike is idling fine in neutral and i turn choke on and reduce air bike will go wot / full throttle.. whats wrong here??? i have been trying to fix this for ages.. there are no air leaks as i have sprayed carb cleaner all over while running and no changes... can it be something in the carb? can in the the choke? any ideas????
 

69ST

Well-Known Member
i have a 1985 ct70 - new air filter , new spark plug, carb is fine etc..fuel flow good i am having a problem with the bike stalling while in first gear and sitting idle...the bike idles fine in neutral - but when in first gear will stall... i turn up idle and turn in air screw..... all good on idle - idles perfcet - the choke is very sensetive... if bike is idling fine in neutral and i turn choke on and reduce air bike will go wot / full throttle.. whats wrong here??? i have been trying to fix this for ages.. there are no air leaks as i have sprayed carb cleaner all over while running and no changes... can it be something in the carb? can in the the choke? any ideas????

Nope, if the carb was fine, it wouldn't be doing this. "Turning on" the choke would make the engine run richer, the choke butterfly being a second throttle valve, upstream from the slide. Sounds like you've gotten the engine to sort of run, with the choke applied, i.e. closed. That compensates for whatever is making the mixture lean (something clogged inside the carb) and restricts airflow enough to keep the rpm down. When the choke is opened, airflow is no longer restricted, the engine revs-out. Unless there's something messed-up with your clutch, there should not be enough clutch drag to stall the engine. As rpm drops down to a (very) fast idle, the centrifugal assembly should disengage.

Insufficient fuel in the pilot (idle) circuit will result in a weak/unstable idle. Insufficient fuel in the main circuit will result in weak throttle response and bogging, above idle.

Verify point gap and compression. Point gap should be around 0.016". If it's too narrow, the engine can't run right. Once that's taken care of, time to verify compression. A leaking valve, intake especially, can cause the issues you're getting. I'll spare you the tech lecture behind this.
 
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