I checked mine last Fall and was happy to have 20" of vaccum for the wipers.
If you are trying to debug the system and get your wipers running well, I would suggest first running a line just to the wiper motor itself, by passing the washer switch entirely.
Use new hose, put a little grease on any connections to eliminate leaks.
Whatever performance of the wipers you then get is your "best case" scenario, short of sending the motor out for rebuilding.
The switch is, almost without question, a potential source for leaks and thus reduction in performance. If you decide to keep it, carefully check it out and perhaps use some RTV or other sealant.
Check your hoses for cracks (they could be 60 years old!).
I had my motor rebuilt over 10 years ago by Fricken and it still works really well, with the current 20" driving it.
PS should you happen to get a fuel pump rebuilt, a good shop can fiddle with the geometry of the arm for the wiper vaccum and gain some additional vaccum over stock.
Last edited by JohnG : 04-23-2017 at 08:21 AM.