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

Nipple purpose and accurate seating guidance

The O.S. Engine OS23754721 No.18 carburettor nipple is specified for RC carburettor assemblies as the interface for the needle and seat, controlling fuel admission in low-speed and idle circuits. The No.18 size ensures correct compatibility with matching needles and seats.

Fitment is straightforward: remove the carburettor top, withdraw the old nipple and any seat, then press the new nipple into the designated bore until seated flush. Use appropriate small tools to avoid deforming parts. After fitting, confirm unrestricted needle movement prior to full reassembly.

During tuning the nipple helps maintain needle alignment so that changes to main jets or low-speed settings yield repeatable results. Keep nipple seating consistent while testing different setups to isolate the effects of other adjustments. Regular inspection prevents blockages or wear from affecting metering.

Service notes: clean passages with suitable RC cleaners, avoid abrasive implements that alter dimensions, and replace the nipple if you detect scoring or deformation that could compromise fuel metering.