Husqvarna TC 250 2010 Workshop Manual page 50

SETTINGS AND ADJUSTMENTS
Assembly
Grease the edge (C) of the filter face that goes into the housing to ensure proper
sealing. When refitting the filter into its housing, make sure to position it with
the tab (A) pointing upwards and edge (B) at the left bottom corner of the filter
housing. Refit any parts you have removed.
An improperly positioned filter might let dirt or dust into the engine, leading
to early wear of piston rings and cylinder.
A = Upper side
B = Left-hand side
D.20 Part. N. 8000 H1489 (10-2009)