My choke has been failing lately, so I started adjusted the idle screw, it seemed to be set a bit high. It seemed to help, can anyone confirm that this was correct? Does idle affect the amount of air or fuel delivered to choke?
Adjusting the idle screw does affect the behavior of the engine while the choke is engaged.
The choke prevents the plastic slide from lifting meaning that all the air to the engine has to squeeze through a small area over where the idle jet feeds fuel into the air stream. The air speeds up as it squeezes under the plastic slide and thus picks up more fuel through the idle jet.
(https://i.ytimg.com/vi/DbzWS76bpfU/maxresdefault.jpg)
The idle screw sets the minimum angle for the throttle valves. Raising the screw increases the amount of airflow through the carbs while the throttle control is in the relaxed position. Raising the idle screw is identical to twisting the throttle a tiny, tiny amount.
Thanks for the thorough explanation, sounds like you know this engine well. If I can ask another question, what's the purpose of the portion of the float in this pic:
http://i.imgur.com/1nWtlg1.jpg
The o-ring must seal something, but I don't have disassembled at the moment to figure it out. Someone suggested it's delivering fuel to the choke passage, along with the pilot jet, but it didn't sound right.