Rotax 914 Series Maintenance Manual page 119

Always replace both spark plugs of a cylinder and do not interchange spark plugs
between cylinders.
Remove the spark plugs and store them according to cylinder and position.
Spark plug face reveals the following about the operating condition of the engine:
light coloured to brown:
plug and calibration of the engine are correct
velvet black:
Indicates the following:
- mixture too rich
- insufficient air intake (clogged air filter)
- engine operating temperature too low.
oily, glossy coating:
Indicates the following:
- misfiring
- too much oil in combustion chamber
- worn cylinder and piston rings
white with formation of melt beads:
Indicates the following:
- mixture too lean
- leaking valves
◆ NOTE:
Effectivity: 914 Series
Edition 1 / Rev. 0
BRP-Rotax
MAINTENANCE MANUAL
Operation with leaded fuels (e.g. AVGAS 100LL) can result in
increased wear of the spark plugs. Reduce renewal intervals
accordingly.
12-00-00
page 45
May. 01/07