Os-engines 2B Carb - 22681005 User Manual download pdf

O.S.2B.2CA.2CB.2H

INSTRUCTIONS FOR O.S. TYPE 2B, 2CA, 2CB & 2H AUTOMATIC CARBURETTOR

This new carburettor incorporates an automatic mixture control device which ensures that the engine receives a

correctly balanced mixture of fuel and air at all throttle settings. The device progressively reduces the effective

size of the fuel jet orifice as the throttle is closed, thereby preventing the engine from running too rich at low

speeds. This also means that an airbleed is no longer required and, with its elimination, maximum suction is main-

tained at the fuel jet at all times. This is a most important factor where manoeuvres have to be executed at low engine

speeds and through wide variations of fuel level within the fuel tank.

Under

average

operating

conditions,

the

carburettor

will

normally function satisfactorily as factory set. Simply start the

engine in the normal way and adjust the needle-valve for

maximum r.p.m. On closing the throttle, the engine should idle

at between 2,500 and 3,000 r.p.m. and also run steadily at all

intermediate speeds. However, different fuels and/or climatic

conditions, may require minor readustments for optimum

results.

Throttle Rotor Set-Screw

Needle Valve

Mixture Control Screw

Photo shows carburettor

type 2B. 2CA or 2CB.

mixture control

screw is moved unnecessarily, observe the

re-setting

follows:

(1) Unscrew the throttle rotor set screw and set the rotor at a

position where the rotor hole is completely closed from the

carburettor body hole.

(2) With the rotor set as above, slowly screw-in the mixture

control screw until it reaches the maximum point. Avoid

trying to force it in abruptly. Otherwise, the tapered tip

of the mixture control screw ruins the fuel jet hole. Un-

screw the mixture control screw one turn from the maxi-

mum point.

(3) Re-set the rotor so that the rotor hole opens approximately

0.5 mm (0.02 in.) from the fully closed position. Screw-in

the throttle rotor set screw and fix it with lock-nut.

(4) Do the final setting of the mixture control screw in accord-

ance with the carburettor adjustment stated below.

ADJUSTING THE CARBURETTOR

Three adjustable controls are provided on this carburettor:

(1) The Needle Valve (located on left-hand side of

carburettor).

(2) The Mixture Control Screw (located on right-hand side).

(3) The Throttle Rotor Set-Screw (angled at rear of body).

I. The Needle-Valve is used in the same way as on all model

engines, i.e., for adjusting the high-speed mixture strength.

Start the engine and, with the throttle fully open, gradually

close the Needle-Valve until it is running at its maximum

speed. Caution: Do not close Needle-Valve to too "lean" a

setting as this will cause the engine to overheat and slow up.

Lock Nut

Phot shows carburettor type 2H.

Needle Valve

Throttle Rotor Set-Screw

Mixture Control

Screw

1 2

Summary of Contents

Page 1 - O.S.2B.2CA.2CB.2H

O.S.2B.2CA.2CB.2HINSTRUCTIONS FOR O.S. TYPE 2B, 2CA, 2CB & 2H AUTOMATIC CARBURETTORThis new carburettor incorporates an automatic mixture control

Page 2 - SUBSEQUENT OPERATION AND CARE

Set the Needle-Valve very slightly to the "rich" side of thepeak r.p.m. setting. Make sure that the engine is fully"broken-in" (ab

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Os-engines 2B Carb - 22681005 User Manual

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Summary of Contents

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