400EX Carb on 350X Jetting

[thebutelr]

Hey guys I have a 400ex carb that I was running for awhile but took it off due to not being able to dial it in correctly so I switched back to my stock 350x carb. I had my 350x carb on for about a month and could not get the bike to run right at all so I decided to switch back to the 400ex carb to give it another try. I installed it last night and I am running into some problems again. First off the bike will cut out if I stab the throttle off idle. Second the bike will cut out if I am running down the road and I let the bike's RPM's down and I stab the throttle, this won't kill the bike but it takes a long time to catch up. For jetting I am currently running a 138 main jet, 40 pilot, and needle in the middle slot. The bike has the following mods: 10.5:1 wiseco piston, K&N air filter, and a 450r silencer. Any tips on which direction I should take on my jetting? Thanks in advance.

[Vealmonkey]

What does the spark plug look like? That is the real story. If it's black, then you will have to go smaller jets, iif it's white, then you have to go more. But you have to remember, you have 2 jets in your carb and you have to tune both jets in.