OK, so just to confirm. I should order for my 2009 KLX250sf (soon to be a 351) with a KDX200 snorkle and FMF Q4 End can...

The DJ 2206 kit, which is made for a KLX300. and spec'd as a Stage 2..

Contents
1 Main Jet DJ120
1 Main Jet DJ124
1 Main Jet DJ128
1 Main Jet DJ132
1 Fuel Needle DNO352
1 E-clip DE0001
2 Adjusting Washers DW0001
1 Slide Drill DD 32
1 Plug Drill DD 5/32
1 Screw DS0001

Cos if so, I'll just order it now.

 

Doc, I'd bet a nickel that the 300 kit will be more suitable for your 351. You're letting in more air with a KDX snorkel, you're opening up the exhaust with the new muffler, and you're upping displacement to 351. If this was my project, and my money, and I had a question as to which jet kit to use on my modded engine, I'd call DJ. Ask them which kit will be more suitable for your 351. I'd use the 300 kit stage 2, as I'll bet another nickel that it will be more suited to a 351 than the '09 250 kit. Oh wait...I'm using the 300 stage 2 kit in my 300-jugged 250 right now, and it runs great and gets good fuel mileage...LOL! But this is your bike, and you need to feel comfortable with what you run.