246 hard to start

the pump delivery valves (that feed the pump jets) are not supplying fuel to the jets all the time, especially if the car has sat for a week unstarted. I have cleaned them, & shaken them to free the ball inside, which is loose, but after a week seem to stick again.
Has anyone else had this problem?
The 40 dcnf carbs have been cleaned, new gaskets & new pump diaphrams, is the ball sticking & causing this? Remove the jets, shake them & they work correctly for a small time.
Any suggestions or do I need new pump valves? If so where can I purchase them?

Cliff Donnon
South Australia