If the throttle positioner screw is turned in (clockwise) too far; then any adjustment of the idle mixture control screw from seated to removed in your pocket will make no difference, as there is insufficient throttle velocity to activate the idle circuit.

TRY:

(1) Lightly seat the idle mixture screw
(2) Back out the idle mixture screw 1 1/4 turns
(3) Start the engine, and run until at normal operating temperature
(4) Use the throttle positioner screw to adjust the idle RPM to spec

Adjusting the idle mixture screw should now make a difference.

The above assumes the 2100s was correctly rebuilt, and Dr. Goodpliers (the evil twin of Mr. Goodwrench) did not swap parts from a different YF.

EDIT: Just noticed this was your second post. WELCOME!

Jon.

Last edited by carbking; 09/19/2018 3:03 PM.
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