O.S. Engines 4BK Carb - Manual (Page 2)

To return the Mixture Control Valve to its original position, first
screw in the Mixture Control Valve, while looking into the rotor
hole. Then gradually unscrew the Mixture Control Valve until 'A'
is precisely tangential to the rotor hole (i.e. so that 'A' and 'B' are
superimposed) as in the main sketch.
CARBURETTOR CLEANLINESS
The correct functioning of the carburettor depends on its small fuel
orifices remaining clear. The minute particles of foreign matter that
are present in any fuel can easily partially obstruct these orifices and
upset mixture strength so that engine performance becomes erratic
and unreliable.
It is recommended that fuel is passed through a filter when the tank
is filled and that a good in-line filter is installed between the fuel
tank and carburettor and, furthermore, that this filter is frequently
cleaned to remove dirt and lint that accumulates on the filter screen.
Finally, occasionally remove the needle-valve holder from the
carburettor as shown in Photo (2) and extract any remaining foreign
matter that may have lodged in the location shown in Photo (3).
Remove this with
an 8mm spanner
Photo (2)
Dirt and fibrous matter
mostly accumulate here
Photo (3)
P A R T S L I S T
Description
Throttle Lever
Set-screw
Carburettor Rotor
Mixture Control Valve
"0" Ring
Rotor Spring
Throttle Stop Screw Assembly
Throttle Stop Screw
Throttle Stop Screw Holder
Nipple No.1
Carburettor Body
Carburettor Rubber Gasket
Carburettor Fixing Screw
Needle Valve Assembly
Needle Valve Holder Assembly
Ratchet Spring
Needle
"0" Ring
Set-screw
Code No.
4BK
24981405
26381501
24981219
26781309
24881824
26781506
26781619
26681305
26681803
22681953
24981122
22115002
25081700
27881900
27381940
26711305
24981959
24981837
26381501
4D
24981405
26381501
25381203
26781309
24881824
26781506
26781619
26681305
26681803
22681953
25381117
22115002
25081700
27881900
27381940
26711305
24981959
24981837
26381501
5B
26781400
26381501
25181206
26781309
24881824
26781506
26781619
26681305
26681803
22681953
25181111
22115002
25081700
27881900
27381940
26711305
24981959
24981837
26381501
The specifications are subject to alteration for improvement without notice.
6-15 3-chome Imagawa Higashisumiyoshi-ku
Osaka 546, Japan. TEL. Osaka (06) 702-0225
© Copyright 1987 by O.S. Engines Mfg. Co., Ltd. All rights reserved. Printed in Japan
88804