22
In the course of making carburetor adjustments, it is just
possible that the Mixture Control Valve setting may be
upset.
Its basic setting can be re-established as follows:
REALIGNMENT OF MIXTURE CONTROL VALVE
Start the engine, open the throttle fully and set the needle-
valve slightly rich (45-60
°
) from the highest r.p.m. setting.
Close the throttle to the idle position. Allow the engine to
idle for about 5 seconds, then reopen the throttle. The
engine should accelerate smoothly back to full speed.
If, instead, the engine responds sluggishly and emits an
excess of white smoke from the exhaust, the idle mixture is
too rich. Turn the mixture control valve approx. 45
°
clockwise to lean the idling mixture.
On the other hand, if the engine hesitates before picking up
speed or even ceases firing completely, the idle mixture is
likely to be too lean. Turn the mixture control valve 90
°
counter-clockwise to substantially enrich the mixture, then
back again 45
°
clockwise.
IDLE MIXTURE ADJUSTMENT
1.
2.
3.
4.
In paragraphs 3 and 4 above, the 45
°
total movements are,
of course, approximate. It will be necessary to fine-tune the
mixture control screw 10-15
°
at a time to reach the best
setting for optimum throttle response.
Continue re-checking the idle mixture setting until the
engine responds smoothly and positively to operation of
the throttle at all times.
5.
6.
Mixture Control Valve
Carburetor Body
Rotate the Mixture Control Valve until its slotted head is
flush with the carburetor body. Then, screw it in one and
half turns. This is the basic position.
Screwed in 1.5 turns
23
VALVE ADJUSTING
Valve clearances are correctly set before any O.S. engine
leaves the factory and, in normal use, will seldom require
adjustment. However, if, after a considerable amount of
running time, a loss of power is detected, or if he engine
has been disassembled for repair, these clearances
should be checked and reset as necessary.
For checking and adjusting the valve clearances, a VALVE
ADJUSTING TOOL KIT is available as an optional
accessory.
Also, a 5.5mm wrench (not supplied) is required for
this purpose.
• Wrench 5.5mm
• Feeler gauge 0.04mm
The kit comes in a plastic case and includes:
(Code No.72200060)
• Feeler gauge 0.1mm
• Hex. key 1.5mm
• Wrench 5mm
