Vacuum Advance Question...

Cougar Community Classic Cougar Maintenance Restoration and Repair
1

Ok, on a Dual Vacuum Advance unit should both sides be sealed? Meaning, if I suck on each port of the dual advance unit, they should both “vacuum” and not be open to atmosphere, right? Distributor side should be manifold vacuum and the outer side should be ported vacuum, right? So as vacuum changes at each location with RPM the two sides play off of each other and adjust the timing appropriately - at least that is how I understand it.

I’m asking because the 351 / auto that I’m fiddling with has a vacuum advance unit where the distributor side is open to atmosphere - it’s not sealed. I thought it was bad, so I ordered a replacement. Replacement arrives… and the distributor side is also open to atmosphere - it’s not sealed either!
So I go to the SCJ and pull the vac line and give the distributor side a puff… it’s also open the atmosphere >.<

Is my fundamental understanding flawed? If I hook up manifold vacuum to the distributor side of the advance, I’m going to be introducing a vacuum leak…

2

When manifold vacuum goes high on deceleration the distributor side overcomes the ported vacuum and pushes the breaker (POINTS) plate to retard the advance. This is to reduce emissions and prevent backfiring. On acceleration manifold vacuum drops and ported becomes dominant pulling the breaker plate advancing the timing along with the weights. I connected a vacuum pump to both sides of my dual ported distributor and it functions as stated.

3

Yes, since both of them are bad, you would. Luckily those units are easy to find. Summit racing would probably deliver two of them free.


4

Ok, I figured something out. When I pull the arm out on the new advance, it seals the distributor side. By design? Maybe.
I’m guessing once I install the unit on the distributor the arm will be positioned such that the retard side of the actuator is sealed. Maybe.

5

The inner vacuum nozzle goes to manifold vacuum, outer one to port vacuum.

When you check your timing, disconnect both lines and block them off to avoid vacuum leaks.

Don’t get the lines installed backwards.

My setup is like that. Once I put the missing manifold vacuum line back, it really improved a lot.

6

I have found the shop manual usually has a very good explanation of hook ups and function.

7

I used Chilton’s mustang and cougar book. I just ordered and received some other shop manuals, still packaged up.

Now if I could just get one of those transparent distributor caps…

They are a real crowd pleaser but I haven’t seen them in years.