1988 elite runs too rich and cannot adjust

[crowbird]

My 1988 elite will only run a short time without having to clean the plug that is slightly oily but not visibly wet. I have tried starting the air screw adjustment at the 1 3/4 position and gone out from there. When I get out far enough I see dark fuel bibbling from air screw. i have recently replaced carb with one i got on ebay, but suspect it's not OEM. I have checked air cleaner and air path. Iest suspect some air port retriction, so wondering if OEM carb is best? Any other things i shpould check before carb replacement?