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

Mixture control screw for nitro RC engines

This mixture control screw is an RC-scale carburettor replacement part designed for use on the listed O.S. engine models. It serves as the primary adjustable element for fine-tuning fuel/air mixture and idle behaviour on nitro model engines, helping to stabilise idle and respond to throttle changes.

Compatibility is limited to the models named in the product title: 2B, 2C, 21FSR, and 25FSR. The part is intended as a direct replacement for the matching screw in the carburettor assembly and should be used only on model engines of the specified types.

Installation requires access to the carburettor mixture port and replacement of the existing screw with the same engagement and seating orientation. Adjustments should be made in small increments and tested by observing idle stability and throttle response; rich settings will produce a lower idle and sootier exhaust while lean settings raise idle and can increase engine temperature, so changes must be conservative.

For tuning, make baseline adjustments with the engine at operating temperature, then refine mixture in small turns while checking for smooth acceleration and consistent idle. If the engine runs unevenly after adjustment, revert to the previous setting and re-check mountings and air/fuel delivery components for leaks or blockage.