Vacuum advance

Adjustable vac adv units.
From maaaaany years of experience with various brands.
[1] The Crane unit is probably the best known. It is also the stupidest design. Along with Accel [ & I think Mr. Gasket ], there is a spacer inside the spring. If you wind the the wrench in, it locks up! You get no VA. With these, I uncrimp the can & remove the spacer. The best adj VA units I have found come with Chinese dists

[2] VA has two adjustments. Rate, adjusted by using the wrench to change spring tension. And Total or amount of VA added. This requires some form of stop or limiter to limit plunger travel. I have found that in the majority of cases, the total amount will need to be limited. Too much VA [ ported or manifold sourced ] usually manifests it self as light surging &/or slight misfire. The concept of VA then gets blamed [ 'didn't work for me' ] when the real problem is that it was not dialled in properly.

Couple of general comments.

[3] The Crane instructions say to connect to manifold vacuum.

[4] Some of you are probably aware of, or even use, Progression Ignition dists, with models to suit Chrysler engines. Page 4 of the instructions say to connect to manifold vacuum. In upper case letters it says, 'DO NOT connect to ported vacuum'.