Dis-connect the cable housing and see if the needle drops to zero.....
That'll tell ya if its the mechanism or the cable. (I'm voting the cable is pinched some where.....
6sally6
(LOOOOVE a 64 Falcon !! Had one right outta high school)

Sockets are available at Autozoo....Atvance...Napper Auto.... remove the orginal sockets and use MS's favorite (clear RTV) to glue the replacements in. 
I put in TWO sockets in each of my tail light assemblys AND painted the buckets white to make the tailights really bright.
6sally6

https://reincarnation-automotive.com/Duraspark_distributor_recurve_instructions_index.html

THIS ^^^^ is the site I used and it is EZ to unnerstan. (has to be if I use it!)

I also have my curve set up with OUT vacuum advance and a total of 36*
With the lightest springs it goes to FULL (36*) advance under 2000 RPM.
Instant REV off idle and NO spark knock.
I do have a limiter so the timing won't go above 36*.
With 9.5:1 CR and a good battery.. hots starts are a little slow butt..it has never left me. With a manual transmission I don't lug the engine at low speed but....
it will pull right off in 4th gear at 15-20 mph withOUT any spark rattle.
Remember BILLY...around-town cruis'in this as hot a motor as you have...they act a little grumpy.
That's why God made a clutch and lower gears ! 
When it starts to lope a little (like a motor boat going over a wake) Kick in the clutch and clean it out a little.
Maybe down shift of a lower gear!
That's the fun in driving a '-oh no I used a word I shouldn't have--stomp'in' hot rod that MOST guys would die for !!! That's why they all give you 'the Thumbs-up or the Nod' !!
I've noticed NOBODY gives me a thumbs-up or the nod....when I drive the Hyundai. 
6sally6

WOW!!!!!!!!! You have sanded the Mustang so much ...it now looks like a Bronco !!
Oh well......I like Broncos
6s6

25 years ago.....
take your age...
subtract how old you were when you went to the MSBB...
equals 24 years + 1 before you went !
6sally6

Lotta stuff to like about the car aaaaand...... a few things to knitt-pick about.
I would preferred  the rear axle shortened and tuck the tires in aaaaand....a different steering wheel (UU-glee IMHO)
A Mustang with an A/T !?! (what everrrrrr)
I'd drive it !!!
6sally6

Yeah BULLY......what kinda 'cobber-raider" ye got ? Holley ...Holley knock-off...Elder-brock... ??????
Pitcherz are always bedder !
6sally6

TKOPerformance wrote:

Yeah, with an LSA that tight on that profile I'm betting ti just doesn't produce enough vacuum.  If it was 112 or 114 maybe, but I would think there's just too much overlap to produce good idle vacuum. 

ACTUALLY...(Ya I get to do an 'actually'..) the LSA on BILLY's camshaft IS 112*.
It looks like it has 4* ground into it. Equaling 112* Lobe CENTERLINE.
THEREFORE.. ACTUALLY  (WOW!)...it looks to me like a good tune-up on the timing curve and carb would give enough vacuum to run the brakes... (a vacuum leak could be a possibility also)
That 225* of exhaust timing is pretty massive when paired with the 217* intake !
(I bet it REALLY has a Thump! in that idle !)
Those figgerz  are more appropriate when running nitrous! 
Since BILLY ain't 'all-that-and-a-bag-of-chips' when it comes to tuning on his engines
(I don't mean that in an ugly way BILLY....butt-we go back a ways so I hope you unnerstand)
It might be simpler to just go with the vacuum can.
You 'COULD' retard the cam timing 4* or so and shorten the exhaust timing to 221* BUTT that would change the intake timing the same amount and might make it "soggy"(instead of snotty!) 
I'd buy the can.....plumb it in !
6sally6
PS Soooo maybe this does away with my ACTUALLY&THEREFORE...I don't know

(Sorry....this picture makes me look fat !....)
The pic of us 'under-the-hood'...I feel...is a common pose with older Mustangs !
6sally6
If'n y'all ever get to Myrtle Beach SC...pick-up-the-phone....gimme-a-call...we'll-go-fer-a-ride !

BILLY....just for S & G's... post the Lift, Duration@050, and LSA of the cam you installed.
It might help us 'give-you-a-fix' for your vacuum issues.
Also, it might help others when choosing a camshaft with power brakes and/or A/T.
(make this a learning opportunity...sorta-kinda)
6sally6

I like to type phonetically !  That makes the reader(s) really study what I am say'in....(Several of my good friends do the same)
It's almost like a disease !
(that way...no one nose if yew maka mus-steaker knot !)
6sally6

Raymond_B wrote:

"I'd check your idle speed as well, sometimes folks want it real low to get the chop chop..." 

 
People REALLY do that ?!  (how juvenile !!)
6sally6

Welp (thx RPM)....I doubt the websites that have(some) young folks and wimmen stupidly plodding along with their face buried in the screen.... is a Mustang or vintage car forum !
There's always a dab-of-good in any of 'those' sites I suppose.
I don't do My Face or whateverrrr sites. (I do this one and another car site) 
   I look at both sites as a small group of FELLAS sitting around a greasy workshop/garage with maybe an adult beverage and an occasional cigar or dip/chew of tobacco. Just laughing and joking and enjoying our time away from wimmen and computer controlled cars. Where nobody gets bent-outta shape at an occasional burp/fart/or cuss-word or an inappropriate scratch or nose-pick. Just being "the-fellas"...
I'm afraid that won't happen on ding-dong/my face/or ginggle (or whateverrrrrr) 

Is more than one disc a....'discus' ?! (ain't shore!)
6sally6