What size jet kit do I need?

Bought a used FMF Megamax 2 muffler and headpipe recently and was waiting to find out if I need to re-jet my carb for this pipe? What seems to work for you guys out there with 300's? Don't know if this matters, it's a '99. Can i just buy this kit at my local Honda shop? Thanks for the help.
EXScott

[leel]

I just rejetted my son's 300ex after putting on a Supertrapp header and muffler, Uni filter, and 6 one inch holes in the air box (with Univents).

I changed the jetting by:
two sizes larger main jet (two numbers bigger anyway)

dropped the needle clip one slot, which raised the needle. (I'm not sure I would do this part next time)

A half turn further out on the pilot screw


It seems to run great, and starts instantly in cold weather, so it must be close. I ride at 8000-12000 feet in altitude, so the actual jet numbers I use wouldn't help you...

Good luck,
Lorrin