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

Carburettor mixture adjuster for model engine tuning

This mixture control screw is built as a direct carburettor spare for the specified O.S. Engine units. It functions as the adjustable element used to refine the fuel/air mix and tidy up idle characteristics on nitro-powered models.

Compatibility is restricted to the models listed in the product title: 2B, 2C, 21FSR, and 25FSR. The component replaces the original carburettor screw and is intended only for use on those engine types.

Fitting involves accessing the carburettor mixture port and swapping the existing screw while keeping correct engagement and seating. Make small changes and test by watching idle consistency and throttle transition; a rich adjustment will lower idle and darken exhaust, while a lean change raises idle and risks extra heat.

When tuning, let the engine reach normal temperature first, then adjust in gentle increments, checking for smooth acceleration and consistent idle after each move. If performance degrades, return to the prior setting and inspect for air or fuel delivery issues.