This carb was on my yz426 when I bought it. Need jets and dont know what to buy for. I dont see any sort of part number or markings on it anywhere besides the big KEIHIN on the side. I used a caliper and bore indicators and got about 39.5mm. This is a different carb from the 39 fcr that was on my yfz. Whatever it is its pretty trick looking. says "flat cr" on the top. I'm new to the 426, but not the 450. Whats that knob on the bottom left in the last picture?