Derbi boulevard 125 4t Workshop Manual page 155

Engine
â 4.5%, by loosening the screw the CO value in-
creases (rich mixture) by tightening the CO value
decreases (thin mixture).
- If correction of the flow screw position leads to an
increase in speed, adjust the revolutions again and
if necessary the flow screw until stabilised values
are achieved.
- Idle carburetion is considered correct when the
values of oil temperature, number of revolutions
and percentage of carbon monoxide are correct.
Additional information can be obtained from the
analyser:
- the percentage of carbon dioxide (CO2), the per-
centage of carbon dioxide has a reverse trend
compared to the percentage of (CO), values above
12.5% are considered correct. Values out of this
range are considered as an indication of a non-
airtight condition on the exhaust system.
- Unburnt hydrocarbons (HC) are measured in
parts per million (PPM), the value of the HC de-
creases with increased rpm, with the engine idling
it is normal to measure 200
â 400 PPM, these exhaust values are considered
normal for an engine with motorcycle distribution
diagram. Much higher values can be caused by
engine misfiring due to a too thin mixture (low CO),
ignition defects or incorrect distribution timing or a
stuck or non-airtight exhaust valve.
- If the CO is difficult to adjust, carefully check:
- Cleaning of the carburettor
- Correct working order of the automatic starter
- Correct working order of the tapered pin-seat
- Bowl level
N.B.
THE EXTENSION TUBE IS INDISPENSABLE
SO AS NOT TO SEND POLLUTED EXHAUST
FUMES TO THE AMBIENT OXYGEN. IT IS IN-
DISPENSABLE TO USE AN EXHAUST FUMES
ANALYSER PREVIOUSLY HEATED AND PRE-
PARED TO GUARANTEE THE RESET OF THE
ENG - 155