2003 ds650 sputtering mid/high range

[Mountainmanmyke]

hey guys i have a 2003 ds650 and just bought a hmf jet kit with a slip on exhaust with very small restriction and have a k and n air filter with a big gun cdi box. I installed the largest jet that came with the jet kit. I took it out to camp and it sputters mid range and top end. The plugs are black. Should I go a jet smaller? or should I just adjust the air fuel screw and to what? also I was thinking could it be a faulty big gun cdi box? i am not sure, where do i start guys thanks

[yfz48rdr]

Start by going down one size at a time with the main jet. Does the ds 650 have an adj. Needle? You may need to play with the clip setting on this too. Black plugs usually mean you are too rich, or could be burning oil.