Vacuum advance can adjustment

Vacuum advance can adjustment

Crane makes a little plastic cam for limiting the amount of advance for GM/Delco style cannisters.
It comes in this kit Crane Cams 99601-1: Adjustable Vacuum Advance Delco Point Type | JEGS
I didn't think it would work with Chrysler type internals.

JG1966 said
I was always under the impression that on a vacuum advance, the amount of timing is set (double what's marked on arm) and you are adjusting the amount of vacuum needed to make the timing come in.

Correct.

JG1966 said
My 340 MP distributor from Jegs (part no. 40500) says it's the other way around, at least according to paperwork. Has anybody used one of those?

I have not. Do the internals use Chrysler style mechanism?

JG1966 said
On instructions, it says "The vacuum advance canister is factory set to produce 5-7° of crankshaft advance at 15” of vacuum. .... Turn the wrench clockwise to increase the amount of vacuum advance or counter-clockwise to decrease."
That sounds wrong in a couple of ways. For one, I think it should read 10-14° of crankshaft advance. Also, I only get about 12" of vacuum at idle (I'm using manifold port), so if the 15" isn't adjustable, it doesn't do me much good. I called Jegs and didn't really get clarity on it

If could be plain wrong as you suspect, or they may have set it so vacuum begins to add advance around 10 to 12*. In that case, it might only have added 7* degrees at 15"; and to hit the maximum advance it can add might take 20" Hg. That's what was found on this older Chrysler built distributor with the adjuster 6 turns ccw.

JG1966 said
I guess my question is do they make vacuum advance with adjustable timing degrees rather than vacuum needed OR are these instructions maybe inaccurate?

Only way to make the maximum advance adjustable I've seen is to drill the casting and tap it for a screw. This is the method Mderoy340 used and is shown in How To Limit and Adjust Chrysler Vacuum Advance Cans