mercarb 2bl accel pump check ball?

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I took my neighbors 2bl mercarb apart tonight becuase after 2 trips to the local rebuild shop it still didnt work right...upon inspection i noticed there was no screen,clip and check ball in the bottom of the accelerator pump fuel well?We had 3 different manuals including a mercriuser one that all showed these parts in the exploded views?I rebuilt mine a few years ago and cannot remember but i seem to think mine had these parts..are they simply missing or are they not always used? do they come in a sierra carb kit or have to be ordered individually?..any help would be appreciated..thanks