I have bought a 2001 400ex and am wondering if it is running lean. I have a white bro e series exhaust. i have tried larger main jets which seem to help the high end of the band of course, but I have also not been able to perfect killing the engine while throttle is pressed and pull the plug.

the fuel mixture screw is 2.5 turns out

When I pull the plug after it is warmed up and I let it idle for a while it is white. When i let it idle with half choke, the plug is tan.

THE PREDICAMENT: I can turn the fuel mixture screw all the way in and the engine does not die.

I am new to tuning the carburetor and was thinking of maybe trying a 40 or 42 pilot jet. But without the engine dying when the fuel screw is turned in all the way, I am at a stand still.

Any help or suggestions, tips or tricks would be appreciated thank you!