O.S. Engine OS22681320 Throttle Stop Screw for 20D 20F 2FB carburettor adjustment  [OS22681320]

Throttle stop screw overview

This throttle stop screw is a small replacement part intended for use on RC model engine carburettors identified by the 20D, 20F, and 2FB model designations. It serves as the adjustable contact that limits the throttle valve closed position to set consistent idle and to help stabilise needle adjustments during tuning.

Fitment follows the original carburettor layout for the listed O.S. engine models, where the screw bears against the throttle stop tab or cam surface. Installation typically requires backing out the existing stop, seating the new screw in place, and setting the idle by turning the screw in small increments while the engine is cold or at idle, then fine‑tuning with the main and idle needles as needed.

For practical tuning, use small increments and verify throttle return and idle stability after each adjustment, and confirm the throttle linkage clears all stops throughout the travel. Keep the area clean from fuel residue and inspect for thread condition to ensure reliable repeatable settings.