O.S. Engine OS23754721 No.18 Carburettor Nipple for Tuning  [OS23754721]

Purpose and correct seating of the nipple

The O.S. Engine OS23754721 No.18 nipple is produced for RC carburettor assemblies and functions as the interface for the needle and seat. It controls fuel admission at idle and low-speed circuits and must match needle geometry for predictable response.

Fitting requires basic carburettor handling: remove the top cover, extract the old nipple and any seat parts, then press the replacement nipple into the designated bore until it is fully seated. Use care with hand tools to prevent distortion. Verify needle travel before completing reassembly.

In tuning practice, a correctly seated nipple keeps needle alignment consistent so changes to jets or needle selections produce measurable effects. Maintain nipple condition to avoid masking other tuning variables.

Care guidance: clean passages with approved RC cleaners, avoid metal abrasives that alter shape, and replace if any scoring or deformation is visible that could disturb fuel metering.