O.S.Engines 7B 26781008 Manual

About this manual

This manual provides instructions for the O.S. Type 7B automatic carburettor (models 5B, 4BK, 4E). It explains how the device ensures a correctly balanced fuel-air mixture by progressively reducing the effective size of the fuel jet orifice as the throttle is closed. This feature prevents the engine from running too rich at low speeds and eliminates the need for an airbleed.

What's inside

• Automatic Mixture Control
• Adjusting the Carburettor
• Needle-Valve Adjustment
• Mixture Control Screw
• Throttle Rotor Set-Screw
• Carburettor Insert Installation
• Operation and Care
• Parts List

Specifications

Frequently asked questions

How do I adjust the high-speed mixture strength?

Start the engine with the throttle fully open and gradually close the Needle-Valve until it runs at maximum speed, then set it very slightly to the "rich" side of the peak r.p.m. setting.

What indicates that the idling mixture is too rich?

If the engine begins to idle unevenly, hesitates before picking up to full speed when opening the throttle, or puffs out smoke and stops when closing the throttle.

How do I adjust the minimum idling speed?

Turn the Throttle Rotor Set-Screw counter-clockwise if the engine runs too fast with the throttle closed to allow the throttle opening to be reduced.