PIAGGIO 500 cc Service Manual page 210

Fuel injection
When the CO percentage is correct and the HC (PPM) value is greater than the maximum allowed limit, check:
- spark plug
- valves play
- timing phase
- exhaust valve seal
If it proves necessary to replace the control unit it is important to carry out TPS reset and preventively preset the
trimmer value of the original control unit (if available).
In all cases check the CO value again.
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