1977 atc90 carb issues

[Lucas_riley]

Just acquired a 1977 atc90 that had been sitting for a few years. Bike was said to be running when parked. When I got it, I thoroughly cleaned out the tank, replaced gas lines to carb with clear gas lines and added an inline filter. After taking the carb apart and cleaning the bowl, jets, as well as the little filter in the side of the bowl, I put everything back together. Also put in a new spark plug. When I turned the gas on, after about 30 seconds, gas started slowly dripping out the back intake side of the carb. So I took it apart again, inspected the float, then tweaked the tab on the float that presses on the needle valve and made sure it made a tight seal when the bowl was full to not allow gas through.
Once put back together again, when I turned on the gas petcock, it didn't leak where it had before. After a minute or so, i gave it full choke, and it started after 3-4 pulls. It runs on full choke and will idle on its own, but refuses to stay running when I back off on the choke.
I am trying to tune this carb to avoid buying a new $50 carb. Does anyone know the factory settings on the idle speed/mixture screws? How many turns out, etc.
goal is to obviously make bike idle on its own, and respond to throttle response.
Help? Has anyone found a fix to this issue?
Thank you

[Pickup_man]

My first suspicion would be the float tab that you adjusted. Improper float height can cause some running issues. If the float is too low you're carbs will not fill fully with gas causing less gas to get to the motor causing a lean condition. By running on choke it cuts off some of the air flow allowing the motor to run. When you turn the choke off too much air is getting to the engine and killing it. This is just my thoughts and I'm no expert, but I would start with getting a new float needle, adjusting the float tab back to where it was and starting there. I'm not sure about screw adjustments but here's a link to service manuals that should provide that info. http://www.oscarmayer.net/atc/manuals/ Good luck!

[Joseph Farrow]

The proper way to adjust the air and idle is to screw the air all the way in and idle it up until it will stay running. Then slowly open the air while backing off the idle until it smooths out. Usually the air is out around a half to three quarters of a turn.

[effort=results]

Also check your compression. My 90 acted like that and i had a snapped ring.

[coolpool]

I can safely say if you plan on owning one of these machines you;ll need a manual. They are available for download on this site. Get your float height right (somewhere around 20mm if i remember correctly) and pre-adjust your air/idle as the manual states. Then you'll have somewhere to start.