Flat Slide Carb?

[ds450]

Im working on my friends 400ex and it doesnt seem to be jetted right. He bought it like this. It has a 440 kit, oversized valves, stage 3 cam, yoshi exhaust, rev box, no air box lid. The person before him installed a keinin FCR 39mm carb for the 400 and im not sure about where I should start the jetting to get it right. It has a 168 main in it. I saw on here that somone had a 185 in their flat slide carb on a 400ex.

Can anyone tell me about where to start the jet sizing? Thanks

[drew416ex]

Tell me the color of the spark plug and how does it run at various rpm. Idle - 1/4 throttle, 1/2 throttle, full throttle? I have a 39 fcr so maybe i can help. Also what size pilot is in it and what position is the clip in on the needle?