I would try this - wind in the air/fuel needle in the throttle base til it bottoms out (gently, or you could damage the tip of the needle) then adjust it out 3/4 of a turn to start off with. Then try adjusting the air bleed screw above it next to that vac barb in your pic until it starts to make a difference. This only affects the idle mix but if you can get an improvement on the idle you stand a better chance of adjusting everything else. If the air/fuel needle is sealed so it can't be adjusted - I got nada