Is the delayer spring the correct length? When installing the spring on the pump you will notice that it’s compressed. The spring doesn’t push the pump down, but acts as a delayer cushion so the pump doesn’t go all the way down at once, especially if you stomp on the gas peddle. The delayer spring allows the pump to move smoothly for a full compression. There is also a return spring under the pump that helps return the pump to its neutral position.

If either of these springs are not installed, or are installed incorrectly you may have a hesitation or pump that won’t move.

There are multiple pumps used on the WW carbs, but this video shows you how to assemble the straight shaft pumps.

https://youtu.be/_NgQUHd2Oks

Other causes include:

• presoaking the pump in oil which can cause it to swell (you can try rinsing it with gas and letting it dry overnight to see if it shrinks back up)
• check the cup for rolling (ie when you install it, be careful not to catch the edge of the pump cup on the edge of the pump well)
• binding in the linkage