Ain't that a kick in the teeth - tearing apart the plumbing looking for an air leak, and it seems the old filter cartridge was the problem. The pump will prime without the cart, looks like old times with the cart installed.
The filter is 135 sq ft, uses 1 1/2" plumbing (rest of system is 2") and is ancient.
Budget rules out buying new, so it's back to craigslist. Found a 175 sq ft C1750 for less than the price of a new cart for the old filter.
After running into the charm of the early Northstar pumps, my radar is up when Hayward's manual does not list the straight 1750, just the 1750s(2), and parts lists show "special" locking knobs and plumbing fittings for it.
So - is this thing a decent filter, or "you'll need special __________" nightmare?