Flapper Mod...What is it??
 

What is the flapper mod and what does it do for ur bike??

The flapper mod is removing the flaps in the intake tubes of the bike, thus giving a less restricting air flow at lower speeds and rpms.

http://www.rogueracing.org/flap.htm

That's for the 04-07 bikes, 08-09 is the same basic thing but a bit harder to do.