APRILIA ATLANTIC 125 Workshop Manual page 93

ATLANTIC 125 - 200
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Using the tester rev counter or a separate rev counter,
adjust the idling screw until reaching a rpm value of
1700 ÷ 1800 g/min.
NOTE The ignition system produces a big power. In case
unsuitable rev counters are used, some reading errors may
arise. The rev counter is suitable for this operation whenever
it can take readings also at high rpm values, such as 6000 ÷
8000 rpm.
•
Adjust the flow screw until reaching a CO rate of 2,5 ÷
3,1%. To increase the CO rate (rich mixture) loosen
the screw, while to decrease the CO rate (lean mixture)
turn the screw in the opposite direction.
•
If the rpm value increases after the flow screw
adjustment, adjust the rpm value again and, if
necessary, adjust also the flow screw until reaching the
recommended values.
•
The idling mixture is correct when the oil temperature,
rpm and CO values are respected.
•
The tester gives further information, such as:
- Carbon dioxide (CO ) percentage. This value is opposite
2
to the CO rate, namely with correct values above 12.5%.
Non-conforming values indicate that the exhaust system
is not perfectly sealed.
•
Unburnt hydrocarbons (HC) measured per million
(PPM). The HC value decreases as the rpm increases.
With the engine at idling speed, the standard value is
of 200 ÷ 400 PPM. These values apply to an engine
with motorcycle timing diagram. Values far above
these limits can be caused by engine misfiring due to
too a rich mixture (low CO rate), ignition defects,
improper timing or jamming or unsealed exhaust
valves.
Should some difficulties in the CO rate adjustment arise,
carefully check:
- Carburetor cleaning
- Automatic starter operation
- Seat-tapered metering rod operation
- Float chamber level adjustment.
FUEL SYSTEM
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