i have an 09 klx250s and live in long island ny which is about sea level.. have installed the two bros m7 carbon slip on and a uni air filter and the bike seems to be running fine... i have the dynojet stage 1&2 jet kit but dont know which main to install especially because the bike seems to be running quite well except for the backfiring on the decel, but im told thats normal... also when installing the kit should i remove the snorkel? or the whole airbox lid? i never really encounter any deep water around here but the stock filter looked kinda dirty and ive only had the bike for 3 months... also i dont know which main jet is stock on the bike.. mrcycles says #118 but the dyno jet kit has jets from #112 to #132 and the instructions are very basic http://www.dynojet.com/pdf/2152.pdf

 

128 main, clip on third notch from the top of the needle, either drill the slide OR use the weaker spring in the Dynojet kit.

PULL OUT the snorkle and leave it open...if you want to buy a KX200 snorkle, that's OK, but, it's not required.

I believe the air screw starting point is three turns out. It's nice to have a "t-handled" screw (such as is made by Kouba) to put in place of the stock air screw, as it makes it easier to fine-tune.

You may find your deceleration popping isn't changed much, if at all, by this Stage 2 upgrade. To get that popping to go away may require a slightly larger Pilot Jet. But, it's not going to hurt anything as long as it is mild. Make sure your exhaust flange is tight, though, if you have more than just mild popping....as a leak there can sometimes exacerbate a pop.

I get low 60 mpg with this setup, almost never any decel popping. Have HMF with Quiet Core and spark arrestor screen, smog stuff eliminated, no snorkle.