jetting question

ok, i just put on a new bolt-on and i need to reject (pops upon deceleration, means i'm running lean right?). i've heard all they need to do is "shim the needles" to richen it up so you don't have the pops. do i need to buy a jet kit to fix this or does this not require a jet kit?

i'm hoping to hear a no or if not, anyone know where i could get one nice a cheap? i just bought a track bike and also have collage tuition due beginning of december.

any info in this would be greatly appreciated!