OK,but don't think That's a problem here.
Get the engine to where it is warm and will idle.
Disconnect the linkage to the carbs. Use springs, weights, elastic bands to hold the throttle plates in a closed position.
back one throttle plate screw out till it's not touching and the butterfly is completely closed (assuming the butterfly is properly fitted in the throttle shaft). close the idle mixture on that carb.
Start the engine and adjust the 2nd carb to the proper idle RPM and set the idle mixture using a vacuum gauge. When it's perfect, carefully mark the position of the idle air and throttle plate screws. shut off engine and close the idle air and back out the throttle screw till the plate is closed.
Repeat the procedure on the first carb.
When done return the idle air screws to their set positions. Return the throttle screws to their set positions. start the engine.
back out each throttle screw in small moves until the idle speed is correct.
I usually do a final check with a piece of hose up to my ear and listen to the air flow in each carb in case it needs a final tweek.
Carefully link the carbs together without changing anything.
