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

Carburettor nipple role and correct fitment

This O.S. Engine OS23754721 item is the No.18 carburettor nipple intended for RC carburettor assemblies. It interfaces with the needle assembly and helps regulate fuel flow through the low-speed and idle circuits. The No.18 size identifies the mating geometry for corresponding needles and seats.

Installation is straightforward for modelers with basic carburettor experience: remove the carburettor top, lift out the worn nipple and seat if present, then press the new nipple into the bore until it sits flush. Use small, appropriate tools to avoid deforming the nipple or the carburettor body. Confirm that the needle moves freely after reassembly.

When tuning, the nipple supports consistent needle alignment and steady fuel delivery. If you change needle sizes or experiment with main and low-speed jets, keep nipple seating consistent to isolate other variables during tuning sessions. Regular checks for blockages, varnish, or wear help maintain reliable carburettor response.

Maintenance tips: clean the nipple and nearby passages with approved RC cleaners, avoid abrasive picks that could alter dimensions, and replace the nipple if you find scoring or deformation that affects metering.