The common Dellorto has no adjustment for fuel/air....it has only an idle adjustment. By screwing that screw in while you look thru the throat of the carb.,you can watch the slide open slightly a crack at the bottom...........a one millimeter gap is plenty for initial idling adjustment.
If it's bogging at start-up, you could have a plugged main jet or emulsion tube.
Also,a wet plug can be a BAD spark plug. Did you replace it? don-ohio