O.S. Engine OS22481619 Mixture Control Screw for 2B 2C 21FSR 25FSR  [OS22481619]

Precision mixture screw for O.S. Engine carburettors

This mixture control screw is an RC-scale carburettor replacement designed specifically for the O.S. Engine models listed. It is the main adjustable component for dialing fuel/air ratio and stabilising idle behavior on nitro model engines, aiding throttle response and low-speed running.

Use is limited to the models named in the product title: 2B, 2C, 21FSR, and 25FSR. The item is intended as a direct replacement for the original carburettor screw and should only be fitted to engines of those specified types.

Installation requires access to the carburettor mixture port and the removal of the existing screw while keeping the same seating orientation. Make small adjustments and observe idle stability and throttle response; overly rich settings lower idle and darken exhaust, while lean settings raise idle and can increase engine temperature, so proceed conservatively.

For effective tuning, warm the engine to normal operating temperature before making baseline adjustments, then refine in small turns while checking for smooth acceleration and a steady idle. If running becomes irregular after changes, revert to the previous setting and inspect mounting and fuel/air delivery for leaks or obstruction.