03 yz40f running lean?

My new to me bike is running poorly. Wont kickstart(have to jump it), has a huge hesitation, and pops off throttle. All leading me to believe it is running lean. Now how can I fix this? I tried the adjustment screw on the bottom of the carb, and whether in or out and everything in between it still ran horrible.

Mods:

Full DR. D exhaust

Swiss cheesed airbox

Boyesen acc. pump bowl

I cleaned the carb, reset timing, checked valves, and did an oil change/spark plug swap and it got me nowhere.

Sure the valve clearences are good?

Fuel is fresh?

What happened, no matter how insignificant, sionce it ran properly?

Sure the valve clearences are good?

Fuel is fresh?

What happened, no matter how insignificant, sionce it ran properly?

Valves seemed ok, a little tight on the intake side. If that is a possible culprit I drop the bike off at a shop to have them do it as I tried to figure it out and had a bit of a tough time when thumbing through the manual

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