Ducati 749S 2002 Manuel D'utilisation Et Entretien page 164

Cleaning and replacing the spark plugs
Spark plugs are essential to smooth engine running and
should be checked at regular intervals. Spark plugs
condition provides a good measure of engine condition.
Have the spark plugs inspected or replaced at a Ducati
Dealer or Authorized Workshop. Firstly, they will check
the color of the ceramic insulator of the central electrode:
a light brown, even color is a sign of good engine
condition.
E
Secondly, they will check the central electrode for wear
and measure electrode gap. Electrode gap should be:
0.6-0.7 mm.
Important
An electrode gap outside the specified limit will
adversely affect engine performance and may lead to
difficult starting or erratic idling.
74
(fig. 79)
0,6 ÷ 0,7 mm
fig. 79