O.S. Engine OS4A408120 61HB GGT10 Carburettor Rotor - Replacement for O.S. Carburettors  [OS4A408120]

Overview of the rotor's role

The O.S. Engine OS4A408120 rotor with code 61HB GGT10 is designed as a like-for-like replacement for matching O.S. carburettor bodies on RC nitro engines, restoring the rotor contour that meters fuel and air.

In service the rotor determines the mixture progression through the carburettor throat and therefore affects throttle feel and idle control. Check that the rotor marking and indexing features align with your carburettor before fitting.

Installation guidance: take off the carburettor top and remove the old rotor while noting its orientation, inspect the slide and needle for signs of wear, then install the OS4A408120 so its index marks match the housing. Conduct bench checks of idle and midrange and make conservative needle changes to dial in mixture.

As a tuning component the rotor can alter throttle transition and response; replacing a worn profile can help return consistent throttle behaviour. Maintain cleanliness and correct gasket placement to prevent air leaks that could mask rotor performance issues.