Usually, if the engine takes a while to come down to idle when you close the throttle, the idle mixture's a bit too rich. The idle should be set only after the high-speed needle's leaned to just rich of peak RPM. You may also need to rotate the spraybar a hair.

Fuel should be 5%-10%, oil can be 10%-12% once the engine's had a few gallons of regular fuel run through it.

Please see the thread on setting the carburetor that's one of the "sticky" messages at the top of this forum.