New to me 85 xr350 with single carb, kicks over cold (never hot), bogs down on acceleration. Messed with air screw, removed carb and cleaned. Same problem. Finally, took off air filter and it ran much better. Not great, but could hit acceleration. Lot's of exhaust tho. What's the deal? Should I rip out airbox and put on slip on air filter? Am I rich or lean? I can't tell as I'm just aimlessly turning the screw back and forth. Why is it good with no air filter?