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

Carburettor nipple function and fit

This O.S. Engine OS23754721 item is the No.18 carburettor nipple specified for use in RC-scale carburettor assemblies. It serves as the interface for the needle assembly and governs fuel passage at the low-speed and idle circuits. The No.18 designation identifies the sizing used to match corresponding needles and seats.

Installation is straightforward for hobbyists with basic carburettor experience: remove the carburettor top, extract the old nipple and seat if present, and press the replacement nipple into the correct bore until seated flush. Use appropriate tools for small parts to avoid deforming the nipple or the carburettor body. Confirm needle free movement after assembly.

In tuning the fuel map, the nipple plays a supporting role by ensuring consistent needle alignment and fuel flow characteristics. When swapping needle sizes or testing main and low-speed jets, retain consistent nipple seating to isolate variables during tuning sessions. Regular inspection for blockages, varnish, or wear helps maintain repeatable carburettor response.

Maintenance notes: clean the nipple and surrounding passages with approved RC-safe cleaners, avoid abrasive tools that change dimensions, and check for a snug fit in the carburettor bore. Replace the nipple if you observe scoring or deformation that could alter fuel metering.