Re: idle
The mechanical idle stop screw is about halfway up the vertical throttle arm located on the starboard side of that engine, HOWEVER that problem can be caused by the threaded trunion of the throttle cable being out of adjustment where it is clamped to the engine, the three carburetors having the linkages between them out of adjustment, the idle timing adjustment between the vertical throttle arm and the throttle cam being set wrong, etc.
A sticking timer base under the flywheel at full spark advance or a sticking carburetor butterfly would cause the engine to race also. Examine the throttle butterflies carefully along with the timer base and try to find exactly what might not be as it should be.
