O.S. Engine OS4A408120 Carb Rotor 61HB GGT10 Compatible with O.S. Carburettors  [OS4A408120]

Rotor description and purpose

The O.S. Engine OS4A408120 rotor, designated 61HB GGT10, is intended to replace the original rotor in matching O.S. carburettor housings on RC nitro engines, restoring accurate metering geometry.

By controlling the air and fuel flow through the throat the rotor plays a key role in idle quality and throttle response. Confirm that the rotor code and the indexing features line up with your carburettor before fitting to ensure correct function.

Installation notes: remove the carburettor top, slide out the old rotor while noting its orientation, inspect needle and slide for wear, then fit the OS4A408120 so index marks align with the housing. Perform bench idle and throttle checks after reassembly and make incremental needle adjustments if needed.

Proper rotor condition contributes to predictable throttle transition; replacing a worn rotor can restore consistent engine behavior. Ensure all mating surfaces are clean and gaskets are seated correctly to prevent air leaks that can hide rotor symptoms.