anyone have any ideas on what the problem is and what does the small pump on top of the front carb do?
Rods was asking if you used your old spring from your needle and seat valve inside the carb?
Your problem could be your accelerator pump. Witch is the small pump on top of the first carb. You'll need a new diaphragm and make sure the nozzles in both carbs are clear and clean. They tend to get corroded. You can find the diaphragm at SBT.