sounds to me like a pumpshaft/camshaft/crankshaft timing issue or a stuck rack in the governor. Using your shop manual, go thru all the timing procedures shown for the governor to pump (rack) and if needed check all of the gear train for proper timing. You have eliminated all the other possibilities.
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149, 2072, Original, 1772, 1782, #1 cart, Parker 48" sweeper,
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