While there may be other issues, why "borrow trouble"? Some adjustment costs nothing.
The idle circuit is WIDE OPEN at 1.5 turns. 2.25 turns is going to be pig rich, which could cause an erratic idle.
Unless the engine is totally worn out, 1 MAYBE 1.25 turns should be oceans.
Maximum vacuum will always be obtained when the throttle plate is completely closed, as any opening of the throttle plate will be a "vacuum leak".
Suggest start the engine and drive maybe 10 minutes until totally warm. Then set both the idle mixture screw and throttle positioner screw.
Next time you start a cold engine, use the choke as needed until complete warm-up.
Jon.
