Carb tuning, larger accelerator pump nozzle?

Bewy said
Don't see idle speed making a difference, because coming off the clutch you are well above idle speed [ whether 750 or 900 rpm ].
I would reduce the size of the main air bleed. This will bring in the main system earlier because it sounds like there is a 'gap' where the idle cct stops & main system starts.

Just to clean this up, decreasing the size of the MAB will delay the start up of the mains and will make the fuel curve go rich at higher rpm. Increasing the size of the MAB will start the mains sooner and make the fuel curve get leaner at rpm. You have it backwards.