Topic: Correct 68 S Code C-6 Dual Vacuum Advance

[68 S Code]

Trying to get my 68 S code back on the road.As mentioned it is a 68 S code with a C-6, Thermactor and NO AC. The distributor was restored by Tim O'Conner about 6 years ago. At the time I sent it off to him he mentioned that the original dual vacuum advance unit had a bad diaphram, engineering number C8AF-12378-C Autolite B-12 stamping. So he installed an aftermarket single diaphram on it. The current issue is that the car will stall in neighborhood traffic very quickly. Seems to get very hot causing vapor lock. So the question is why?  Although many point to the antiquated original Holley carb (rebuilt and restored) I'm beginning to think its not the carb. I'm being told that if the timing is retarded too by a faulty vacuum advance it will cause the engine to get hotter than it should. That appears to be the problem as it just coasts to a stop and no amount of starter fluid will re-fire it. In my case all that works is cooling down the engine between a 1/2 to an hour and she will re-fire. Real PITA when you are stuck on the side of the road in traffic hoping no one will run into you. I'm leaning towards this being a distributor issue.

This past weekend I replaced the 50 year old Vacuum Advance Control Valve with a new one from NAPA.  Although the routing of the vacuum lines is still in question as the Shop Manual diagram shows one thing but the CJ Forum shows another. I've already pulled the original 50 year old yellow top coil and replaced it with an MSD Blaster 2 which has been temporarily relocated off the intake (to keep excessive heat off it) and mounted it on a bracket off a screw hole from the washer bottle. But I'm thinking that the single port Vacuum advance needs to be replaced with a correct dual. It appears that no one makes a replacement for this application. Tried NAPA, Rock Auto, NPD. Tim O'Connor appears to rebuild these now but his site says he is closed for business. May re-open in October. So what are my options in the mean-time?

[68 S Code]

In addition I read some info on classiccougarcommunity site where Jeff S chimes in and says that the dual diaphram unit is correct.

[Daisy]

The base timing is the timing at idle (when it is stalling) - if I read your post correctly.
So dual or single advance (which only help performance above 1500 RPMs) shouldn't be the culprit... 

The dizzy vacuum advance pot should 'point' to ~7 o clock (as you look top-down). If it points to 7:30 or more to the left - re-time it with a light.

You may just need to address the over-heating.  I had to go to a 4 core radiator. I assume you are using a fan shroud too.
Check the fan clutch (should be 'harder' to spin by hand when hot than when cold).

Also, do you have a phenolic spacer under the carb?

[69SCJQ4.30]

I believe all automatic cars had single diaphragm advances. Don't think a 390 would be any different from 289/302s and 428s with what transmission type had what style diaphragm.

I see that I believed wrong though. Disregard my comment.

[jwc66k]

Try the library.
Jim

[Bob Gaines]

I believe all automatic cars had single diaphragm advances. Don't think a 390 would be any different from 289/302s and 428s with what transmission type had what style diaphragm.

+1 . Out of the ordinary for a  FE with a automatic in a Mustang to have a duel vacuum diaphragm distributor from the factory. Not that it is without precedent . I can only think of 1 SB obscure anomaly, but rarely happened relatively speaking.   BTW what is the distributor number ? I find a C8OF-C but not a C8AF-C for 68 390.  A 390 GT auto would have a C8OF-D duel vacuum. C8OF-C would be a duel vacuum but it is for a 4 speed. Are you sure that it is the correct distributor for the application? The distributors will function regardless of application but they will not work as designed unless in the correct application .

[J_Speegle]

Try the library.

A bit more of a clue - Look under the 68 Mustang Section and then the 68 Vacuum Diagrams - Taken from Ford Documents  pages

Ford shows that they 68 390  4V used the dual port that year with automatic trans but changed to single (like the 478 CJ) in 1969 with automatic applications .

68 IS a confusing year for distributor advance units

68 X code used the single port for their distributors. BTW Ford shows the dual port advance for 289-302 automatic applications when AC was ordered  but also shows J codes with automatic and AC with the single port unit.  But that takes us way off thread

Do agree that you need to confirm what distributor you have currently

Didn't realize that Scott had posted the vacuum routing of 390's over on the 428 site

[Bob Gaines]

A bit more of a clue - Look under the 68 Mustang Section and then the 68 Vacuum Diagrams - Taken from Ford Documents  pages

Ford shows that they 68 390  4V used the dual port that year with automatic trans but changed to single (like the 478 CJ) in 1969 with automatic applications .

68 IS a confusing year for distributor advance units

68 X code used the single port for their distributors. BTW Ford shows the dual port advance for 289-302 automatic applications when AC was ordered  but also shows J codes with automatic and AC with the single port unit.  But that takes us way off thread

Do agree that you need to confirm what distributor you have currently

Didn't realize that Scott had posted the vacuum routing of 390's over on the 428 site

Apparently there is conflicting Ford documentation. It wouldn't be the first time. The pic is a page from the 1968 Ford service specifications manual.It indicates that the 390 distributors used the duel vacuum advance. 68 FE Shelby's used a single vacuum advance.

[J_Speegle]

........... 68 FE Shelby's used a single vacuum advance.

Agreed but being in other engines and applications might just muddy the discussion 

Guess we need to find some examples of how they were built rather than what Ford says they were going to do since those documents don't agree
.

[68 S Code]

Thanks for the responses. The factory manual does show a dual diaphragm for my application 390 GT with Thermactor and no AC in figure 41 on page 9-27 and also the same unit in fig 42 for a manual. However note the differences in vacuum hose routing between the two. Since the rebuild has a single diaphragm vacuum advance unit as Tim O'Connor set up the routing of vacuum hoses to/from the Distributor Vacuum Control Valve is similar to the manual version with a yellow stripe hose from the pass side of the carb going to the top stem, the green hose going to the vacuum advance nipple from the middle stem and the red striped hose going from the front intake manifold fitting to the bottom stem. It is a match to the cut-a-way diagram shown by Scott on the CJ Registry under Distributor Vacuum Control Valve. The cut-a-way at least gives my an idea of whats inside but too bad it doesn't include an arrow showing what happens to the pellet once the coolant temp causes movement. Does the pellet move up or down. I'm guessing up to allow manifold vacuum to take over instead of carb vacuum. Note that in figure 41 the bottom stem shows a small filter. I do have one of those but did not install it as i believe in the large format original 1968 Vacuum and Electrical book i have it shows the the plumbing listed above. But i would have to drag that manual out

There seems to be some confusion so to help clarify the engineering number I gave earlier is not of the distributor but straight off the vacuum advance unit. I agree that the correct distributor is C8OF-12127-D which is listed in the service manual for both 390 GT automatics and manuals however I believe the vacuum advances should be the same as on page 9-39 of the manual the Distributor Advance Specifications do not distinguish a difference between transmissions and on 9-38 it states under Distributor Application that a Dual Advance Dual Vacuum Diaphragm unit is used for both auto and manual.  Regretfully nowhere in the service manual are part numbers or engineering numbers listed for any vacuum advance unit.

Daisy to answer your questions the car does not stall at initial start-up. It stalls after a short drive in the neighborhood with slow side street speed and stop signs. The weird part is that i drove it home about 60 miles (first driving miles in 30 years) last fall after having the a broken rocker shaft bolt extracted (do not rebuild your motor with 50 year old bolts). But once I got off the expressway she seemed to start getting hot and stalled on a side street. had to wait 1/2 an hour and with starter fluid she re-fired but only ran maybe two miles just enough to get home and stalled as i turned up the apron. Two weeks later i tried a local drive in nice cool october temps. Stalled after maybe 5 miles of a little faster streets and only a dozen stop lights. Took over a half hour of cooling and although re-fired it ran horrible the two miles home. parked it for the winter. On Memorial day we tried it again in the neighborhood and died within 2 miles. You can squirt in starter fluid and see it vaporize and drift out of the primaries. I know this engine is tight with less than 100 miles on it but something is causing this excessive heat.

Also I have the following at the carb. Intake manifold, thin grey paper gasket, Mansfield reproduction phenolic spacer, NPD repop thick1/8"  grey felt type spacer with the brass rings for studs. Radiator is the correct C8?Z. I can't remember if I re-cored it and i don't remember how many rows it is. I know I have another factory rad which is the correct size and i had it re-cored with a Modine 3 row but the stamping on the side is for a 69 351 W. That one I know is a fresh re-core which has been in storage since the late 80's.

I've been going back and forth and almost ready to put the original carb in a bin right next to the original smog tube and hoses. They came off when the rocker stud broke. Now its time to check the timing and to see if that Vacuum advance works. Guess what the smog pump has to come off for that. Now i know why smog is so rare to find. Made working on these cars a PITA back in the day. Off to the trash can it went. But mines going back in the Original Parts bin for now.

[68 S Code]

Not only is the original carb questionable but now maybe the distributor. Maybe a hot looking MSD distributor with red wires is in my future if i cant find a dual diaphragm vacuum advance. Are all these Concours cars trailer queens?

[Bob Gaines]

Not only is the original carb questionable but now maybe the distributor. Maybe a hot looking MSD distributor with red wires is in my future if i cant find a dual diaphragm vacuum advance. Are all these Concours cars trailer queens?

No,only the ones that the owners don't want to clean after every drive to keep looking brand new. Many owners want the correct parts on their cars like they were when new but can't stand the thought of not driving them so they do. Don't get discouraged we are all in this together. All you have to do is ask . Sometimes just asking a opinion on what others would do in a given situation can set you in a direction you never thought about. 

[Bob Gaines]

Thanks for the responses. The factory manual does show a dual diaphragm for my application 390 GT with Thermactor and no AC in figure 41 on page 9-27 and also the same unit in fig 42 for a manual. However note the differences in vacuum hose routing between the two. Since the rebuild has a single diaphragm vacuum advance unit as Tim O'Connor set up the routing of vacuum hoses to/from the Distributor Vacuum Control Valve is similar to the manual version with a yellow stripe hose from the pass side of the carb going to the top stem, the green hose going to the vacuum advance nipple from the middle stem and the red striped hose going from the front intake manifold fitting to the bottom stem. It is a match to the cut-a-way diagram shown by Scott on the CJ Registry under Distributor Vacuum Control Valve. The cut-a-way at least gives my an idea of whats inside but too bad it doesn't include an arrow showing what happens to the pellet once the coolant temp causes movement. Does the pellet move up or down. I'm guessing up to allow manifold vacuum to take over instead of carb vacuum. Note that in figure 41 the bottom stem shows a small filter. I do have one of those but did not install it as i believe in the large format original 1968 Vacuum and Electrical book i have it shows the the plumbing listed above. But i would have to drag that manual out

There seems to be some confusion so to help clarify the engineering number I gave earlier is not of the distributor but straight off the vacuum advance unit. I agree that the correct distributor is C8OF-12127-D which is listed in the service manual for both 390 GT automatics and manuals however I believe the vacuum advances should be the same as on page 9-39 of the manual the Distributor Advance Specifications do not distinguish a difference between transmissions and on 9-38 it states under Distributor Application that a Dual Advance Dual Vacuum Diaphragm unit is used for both auto and manual.  Regretfully nowhere in the service manual are part numbers or engineering numbers listed for any vacuum advance unit.

Daisy to answer your questions the car does not stall at initial start-up. It stalls after a short drive in the neighborhood with slow side street speed and stop signs. The weird part is that i drove it home about 60 miles (first driving miles in 30 years) last fall after having the a broken rocker shaft bolt extracted (do not rebuild your motor with 50 year old bolts). But once I got off the expressway she seemed to start getting hot and stalled on a side street. had to wait 1/2 an hour and with starter fluid she re-fired but only ran maybe two miles just enough to get home and stalled as i turned up the apron. Two weeks later i tried a local drive in nice cool october temps. Stalled after maybe 5 miles of a little faster streets and only a dozen stop lights. Took over a half hour of cooling and although re-fired it ran horrible the two miles home. parked it for the winter. On Memorial day we tried it again in the neighborhood and died within 2 miles. You can squirt in starter fluid and see it vaporize and drift out of the primaries. I know this engine is tight with less than 100 miles on it but something is causing this excessive heat.

Also I have the following at the carb. Intake manifold, thin grey paper gasket, Mansfield reproduction phenolic spacer, NPD repop thick1/8"  grey felt type spacer with the brass rings for studs. Radiator is the correct C8?Z. I can't remember if I re-cored it and i don't remember how many rows it is. I know I have another factory rad which is the correct size and i had it re-cored with a Modine 3 row but the stamping on the side is for a 69 351 W. That one I know is a fresh re-core which has been in storage since the late 80's.

I've been going back and forth and almost ready to put the original carb in a bin right next to the original smog tube and hoses. They came off when the rocker stud broke. Now its time to check the timing and to see if that Vacuum advance works. Guess what the smog pump has to come off for that. Now i know why smog is so rare to find. Made working on these cars a PITA back in the day. Off to the trash can it went. But mines going back in the Original Parts bin for now.

Not that it makes that much differance but the C8OF-D is for the automatic and the C8OF-C is for the manual according to the service manual. C8OF-D is not for both.

[sportyworty]

With the 68.5 CJ cars the C80F-D distributor was used initially for the 4 speed with the C70F-F used for the automatic. At some point Ford started using the C80F-D for both applications just using the single pod for the automatic. Somewhat odd but we have come upon this discussion several times over the last decade on the 428 Reg.
The B12 was a generic often found on Cleveland's. The correct vacuum for 4 speed is the HP6 dual port and the automatic single port is the common C5AZ-12370-A

[Daisy]

FWIW:

My early 1967 w/ 390/C-6/Thermactor engine is a single-advance unit.

OP:
Your carb has the correct spacers  - so that answered that...

If the engine is overheating and stalling after a fresh rebuild - "could it be something binding internally."  Did you test turn the engine crank by hand? Does the starter 'struggle' (slow-cranking) when hot?