Distributor Vacuum Advance Issue

[Jay Bee]

While a friend and I were carb adjusting to make my car idle nice he found that the distributor's plate wouldn't budge until 17.5 in/Hg of vacuum. When the distributor was rebuilt and tested advance would start at 7 in/Hg. The vacuum module/diaphragm is fine, holds vacuum no bleeding. The tool he was using is similar to the pictured one. The distributor is a Mopar electronic one.

That's the issue, why does it now take so much more vacuum to get the advance (plate) to start moving? Do those plates eventually bind through time? TIA, John

[Chryco Psycho]

There is a set screw inside the advance unit that can be turned to limit the advance which I often adjust so you have more timing at idle

[Jay Bee]

There is a set screw inside the advance unit that can be turned to limit the advance which I often adjust so you have more timing at idle

He tried several set screws in the opening and concluded that it was a fixed (non-adjustable) vacuum module. Did those electronic distributors come with adjustable vacuum units? Mine is from an electronic conversion kit that was bought in the late 80's, early 90's.

[Skdmark]

The distributor I got with my electronic conversion kit around 1990 came with an adjustable vacuum advance.

[Jay Bee]

I was thinking last night, maybe the vacuum chamber was replaced during the overhaul in 2011. More investigation needed, I need to to find out what size Allen wrench it would have been if the original is still on it.

[73_Cuda_4_Me]

If the vacuum canister has a hex shaped end on it, you can insert a 3/32 allen wrench in the hose nipple. Turning clockwise lessens vacuum needed to advance, CCW increases. My 73 electronic ignition dizzy has the adjustable advance.

More info about setting the vacuum needed for your specific application can be found on line... here is a pretty good one...

https://www.forabodiesonly.com/mopar/threads/how-to-limit-and-adjust-chrysler-vacuum-advance-cans.399753/