I have spent some time attending to the engine of my 2.0 L 1975 with D Jet. It has on occasion just quit as I was cruising down the highway. Thanks to many tips and suggestions form this board I addressed numerous potential problem area. This included points, coil, wiring and proper grounding. I was all excited to take the car to the local Cars & Coffee but never made it for it was acting up just as before but with a bit more regularity. This time I was not as panicked and noticed that the engine occasionally cut out at 2500 RPM when it was under load such as going up a hill. The engine would eventually restart ( similar to a push start ) as I coasted down the side of the road. I have since checked the MPSs and it rapidly leaks down a vacuum. This is a rebuilt unit form AA . I installed it 10+ years & 3000 + miles ago. I also noticed that my vacuum advance diaphragm on the distributor does not hold a vacuum. My question is: are these two issues possibly the source of my problem? My second question is can I just purchase a new / rebuilt diaphragm unit for my distributor since the unit itself seems OK ?

If the MPS leaks down fast the diaphragm needs replaceing and the unit recalibrated. The vacuum can on the dizzy as far as I know can't be rebuilt so find a good used one. Its not that important and wouldn't be the cause of your issues. A failing MPS is going rich as engine vacuum can't pull the diaphragm to the lean position inside so the AFR is wonky.

Send your MPS to Chris at Tangerine and have him rebuild and tune it. It really transformed my street car.

http://www.tangerineracing.com/mpsdiaphragm.htm