TaoTao ATM50 idle fluctuates and stalls

[tahirahmadov]

Hi guys,

My scooter has fluctuating idle, especially when the engine is cold - even stalls when the RPMs go all the way down. When the engine is not completely hot yet, the engine stalls when decelerating. Sometimes when trying to rev the engine when it's cold, turning the gas handle actually kills the engine. After it stalls, I'm not able to restart the engine for a while. Turning the ignition off and on helps.
Under open throttle traveling, the scooter develops top speed (30mph) so the powertrain works fine overall. When warmed up completely (normal operating temperature for an air-cooled engine), the fluctuation becomes tolerable, it no longer stalls.

So far I ensured that vacuum hoses do not leak and adjusted the valve gaps, but that yielded no significant improvement.

Please help!

[Fox]

Adjust the valves and the mixture screw on the carb. You will be happy you did.

Complete valve adjust guide:

49ccscoot.proboards.com/thread/428/valve-adjustment-pics-video-139qmb

If your mixture screw is capped off, you can drill/remove the cap so you can adjust it.

[jkeney]

I had lots of idle issues until I got rid of the petcock entirely and capped the vacuum ports.

[90GTVert]

[tahirahmadov]

Mar 1, 2016 22:05:11 GMT -5 Fox said:

Adjust the valves and the mixture screw on the carb. You will be happy you did.

If the mixture is wrong, why does it work under open throttle and not under idle?

[tahirahmadov]

Mar 1, 2016 22:59:27 GMT -5 jkeney said:

I had lots of idle issues until I got rid of the petcock entirely and capped the vacuum ports.

Do TaoTaos have petcock valves? Where is it located? How does it affect idling RPM?
Vacuum ports - I'm assuming you're referring to the ports left open due to removing the vacuum operated petcock valve?

Speaking of vacuum lines, auto parts store only had a hose which is tiny bit thicker than the original, so the clamps it came with don't hold it tight. I used small zip ties instead. Is that sufficient?

[tahirahmadov]

Mar 2, 2016 8:56:00 GMT -5 90GTVert said:

Thank you!

[Fox]

The mixture screw only affects the idle mixture. It has little to do with the wide open throttle performance. It only meters the idle jet circuit.

A fluctuating idle could be due to a small vacuum leak somewhere so make sure the vacuum hoses are all connected, they don't have any cracks and that the intake boot the carb fits into is tightened to the head and isn't cracked. If all the rubber is good, then the issue is usually the valves and the mixture screw. Once the valves are correctly adjusted and that screw is adjusted properly the idle should smooth out to a steady rate but you have to adjust the screw with the engine idling and warmed up. Read the guide and watch the video:

49ccscoot.proboards.com/thread/429/idle-mixture-adjustment

Petcocks only supply fuel. They don't have anything to do with the idle. If the carb is full of gas then your petcock is fine.