The O.S. Max #7L carburetor does not have a midrange adjustement. Just a high-speed needle and and idle mixture control.

The socket head screw in the middle of the carb only holds the steel yoke onto the mixture control assembly. There is no adjustment. The steel yoke has an oblong hole in it that keys to the mixture control assembly. The socket-head screw just holds the yoke on.

The hex-head scew at the bottom keeps the mixture control assembly from falling out of the carburetor. There should be a small steel washer between the carb body and the yoke with the head of that screw in contact with the steel yoke.

The eccentric-head screw at the top adjusts the idle mixture. Turn left to richen the idle, right to lean it. It doesn't take much movement to affect the idle mixture. That screw rotates from 9:00 o'clock to 3:00 o'clock. 12:00 o'clock is the starting point. Usually, it winds up at the 1:00 o'clock position or so when the engine's been properly-set. That assumes that the high-speed needle's set to just rich of peak RPM.

If you send us an email directly, we can email back the instructions for the O.S. Max .61 SF, which includes the instructions for setting the O.S. #7L carburetor.