Freddie, I'll try to keep this as short as I can....
First- a primer on what the accelerator pump circuit is for
When the throttle plates are opened quickly, most of the time there won't be sufficient airflow through the carb to draw fuel from the main well. At worst, the engine will lean out and stall. At best, it might cough a little, then go. The acc pump is there to "cover up" this time delay in fuel flow, thus providing good throttle response by forcing fuel into the air stream.
Adjustments- pump volume, duration, and timing can all be tuned or modified to optimize the car's launch.
Volume is changed by changing the size of the discharge holes.
Duration is affected by the total volume of the pump reservoir AND the size of the discharge holes.
Timing can only be adjusted on Holleys with different pump cam positions.
On a QJet, the discharge holes must be drilled out in order to change the volume. Once too big, they have to be soldered shut and redrilled. If they're too small, the car will either stall immediately, or hesitate then go.
If the car initially goes, then hesitates, then picks up again, it needs more duration. This may happen after drilling out the holes, as the pump discharges quicker. On a QJet, duration can be increased by drilling additional holes in the pump lever on top of the carb, closer to the pivot. By installing the link from the throttle shaft in one of these holes, the stroke of the pump's plunger will be increased, providing more total pump volume. IF this max's out without satisfactory result, the pump cylinder can be reamed out to accept the 50% larger pump diaphragm from an old Rochester 2GC 2 barrell.
....to be continued... GB
