20D 20F 2FB Carburettor Throttle Stop Screw - OS22681320 by O.S. Engine  [OS22681320]

Overview of the throttle stop screw

This throttle stop screw is a compact replacement designed for RC model carburettors marked 20D, 20F and 2FB on O.S. Engine models. It functions as the adjustable contact that limits how far the throttle valve closes, helping to establish a repeatable idle and stabilise needle adjustments while tuning.

Fitment follows the original carburettor layout used on the listed O.S. Engine units, with the screw bearing against the throttle stop tab or cam surface. Typical installation involves backing out the existing stop, seating the replacement screw, and setting a baseline idle with the engine at rest, then refining while the engine is running.

For practical tuning, make only small incremental turns and confirm throttle return and idle stability after each change. Keep the carburettor free of fuel residue and inspect screw threads for wear to maintain reliable adjustment points.