O.S. Engine OS23754721 No.18 Carburettor Nipple Part  [OS23754721]

Role of the nipple and how it fits

This O.S. Engine OS23754721 No.18 nipple is a direct replacement component for RC carburettors, forming the seating point for the needle assembly and governing fuel flow in idle and low-speed circuits. The No.18 label denotes the sizing used to match needles and seats.

To install: remove the carburettor top, extract the old nipple and seat if installed, then press the new nipple into the correct bore until it is flush. Employ suitable small tools to prevent distortion of the nipple or carburettor body. Ensure the needle moves freely after assembly.

For tuning, the nipple helps preserve consistent needle alignment so you can accurately assess changes from needle or jet adjustments. Keep nipple seating constant when comparing different jetting setups. Inspect regularly for blockages, varnish or wear to preserve predictable response.

Maintenance advice: clean with designated RC-safe cleaners, do not use abrasive tools that alter dimensions, and replace the nipple if there is visible scoring or deformation that could change fuel metering.