O.S. Engines 2BK Carb - 21283020 - Manual (Page 2)

4) Carry out adjustments patiently under actual running conditions,
until the engine responds quickly and positively to the throttle
control.
Note: Mixture adjustments cannot be made accurately under 'no
load' running conditions which, in any case, are not advised
since such running carries a risk of damaging the engine
through over-reving.
5) With the optimum mixture control screw position, light smoke is
visible during high speed running, and the engine revolutions in-
crease smoothly during acceleration.
Remember that, if the engine is operated with the fuel/air mix-
ture slightly too lean, it will overheat and run unevenly. As with
all engines, it is advisable to set both needle-valve and mixture
control screw very slightly on the rich side of the best rpm
setting, as a safety measure.
6) If the engine runs too fast with the throttle closed, the throttle
stop screw should be turned counter-clockwise to allow the
throttle opening to be reduced.
Note: In the course of making adjustments, it is just possible that
the mixture control screw may be inadvertently screwed in or
out too far and its original position lost. In this case, reset
the controls as follows:
First, remove the air cleaner. Then, unscrew the throttle stop
screw until the throttle opening is just closed completely. At
this point, screw in the mixture control screw slowly clock-
wise until it stops. (Do not use force, otherwise the screw tip
will damage the jet hole on the opposite side.) Now unscrew
the mixture control screw one complete turn. Finally, turn
the throttle stop screw slowly clockwise until the throttle
rotor is opened just 1.0mm as shown in Fig. 2 and fix this
setting by tightening the lockout.
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.
O.S. 'Super-Filters' (large and small) are available, as optional extras,
to deal with this problem. One of these filters, fitted to the outlet
tube inside your refueling container, will prevent the entry of
foreign material into the fuel tank. It is also recommended that a
good in-line filter be installed between the tank and carburettor.
Do not forget to clean the filters regularly to remove dirt and lint
that accumulate on the filter screens. Also, clean the carburettor
itself occasionally.
SUBSEQUENT READJUSTMENTS
Once the engine has been run-in (see engine instructions) and the
carburettor controls properly set up, it should be unnecessary to
alter the mixture settings, except to make minor adjustments to
the Needle-Valve occasionally, to take account of variations in
climatic conditions.
The use of a different fuel, however, particularly one containing
more, or less, nitromethane and/or a different type or proportion
of lubricating oil, is likely to call for some readjustment of the
Needle-Valve.
Remember that, as a safety measure, it is advisable to increase the
Needle -Valve opening by an extra half-turn counter-clockwise,
prior to establishing a new setting. The same applies if the silencer
type is changed. A different silencer may alter the exhaust pressure
applied to the fuel feed and call for a revised Needle-Valve setting.
PARTS LIST
Code No.
22481628
22481420
22481449
22681419
21283210
21481200
22481506
21283900
21181976
21283940
21111300
2268)3)0
21283100
22615000
23081706
21283962
2128396)
24881824
Description
Mixture Control Screw
Throttle Lever Fixing Nut
Idle Ratchet
Throttle Lever
Dust Cover
Rotor
Rotor Spring
Needle Valve Assembly
Needle
Needle Valve Holder Assy
Ratchet Spring
Throttle Stop Screw
Carburettor Body
Carburettor Rubber Gasket
Carburettor Fixing Screw
Nozzle Assembly
Locknut
"0" ring
The specifications are subject to alteration for improvement without notice.
6-15 3-chome Imagawa Higashisumiyoshi-ku
Osaka 546,Japan. TEL (06)702-0225
FAX. (06) 704-2722
© Copyright 1987 by OS. Engines Mfg. Co., Ltd. All rights reserved. Printed in Japan
60130010-29607