1968 Carb #7028231 choke pull-off/vacuum break. Is there one or two?

[Andrew Wall CLC#10638]

According to the 68 shop manual, the Deville has just one vacuum break on the carb, near the front fuel line on the passenger side.  However, my 68
Deviille with correct carb 7028231 has two, the second one being at the back of the carb, same side (passenger)
/
I need the front choke pull-off, what is the rear pull off for

[TJ Hopland]

The first (front) one is the one that pulls the choke open slightly as soon as the engine starts.  The rear one has something to do with the secondaries.  I have never figured out exactally what it does.  On my 78 it runs through an air temp switch in the air cleaner so it seems to prevent the secondaries from opening depending on incoming air temp. The manuals also show an option for it to be connected direct to a port on the back of the carb that appears to be manifold vac.  Like that it would seem that they would only need one.  I also know that the rear one was very hard to find and special order but the front one was a stock item in my local store.

[Andrew Wall CLC#10638]

Thanks for the info, I will let me carb expert know!

[cadillactim]

The rear dash pot is not a pull off, it is the idle speed up for the A/C.  Tim

[Andrew Wall CLC#10638]

The rear dash pot is not a pull off, it is the idle speed up for the A/C.  Tim

Isn't it odd that it wasn't depicted in the shop manual?

[TJ Hopland]

Im not sure what Andrew has.  I dont have a 68 car or manual.  My 73's have no such thing and the 73 manual does not show one.  The 77&78 manuals and my 78 has one.  I have owned several Q jet cars that have had them but they were much newer than Andrews.  The 77 book calls them vacuum brakes, front and rear.  On a 77 there is an electric solenoid on the front that bumps the idle if the climate control tells it to.  The only refernce I can find to the rear brake is and adjustment procedure that includes measurement of the choke blade and setting it on the fast idle cam.  Again the 77 manual is the oldest I have that talks about the rear break.  The carb number Andrew gave fits his car according to the charts I have.

Andrew, does your carb have the choke coil on the side of the carb under a round black cover or does it have a rod that goes down to a well in the intake?

Here is a pic of the one off my 78, its partially apart and missing a thing or two.  The part highlighted in red is the part I think we are talking about.  The choke is the black thing inbetween the brakes.  In 75 the cads started using the electric choke like the one in the picture.  I think the 74's used one that looked the same except for it didnt have the electrical connection and had a tube that ran into it from the manifold. As far as I know the 68-73's had the choke coil in a well in the intake manifold and a rod that goes up to the carb.

[cadillactim]

Look in the air conditioning section of the shop manual, there it will show the vacuum line going to this dashpot (will not show picture, but will show vacuum diagram with dashpot).  Tim

[Andrew Wall CLC#10638]

Im not sure what Andrew has.  I dont have a 68 car or manual.  My 73's have no such thing and the 73 manual does not show one.  The 77&78 manuals and my 78 has one.  I have owned several Q jet cars that have had them but they were much newer than Andrews.  The 77 book calls them vacuum brakes, front and rear.  On a 77 there is an electric solenoid on the front that bumps the idle if the climate control tells it to.  The only refernce I can find to the rear brake is and adjustment procedure that includes measurement of the choke blade and setting it on the fast idle cam.  Again the 77 manual is the oldest I have that talks about the rear break.  The carb number Andrew gave fits his car according to the charts I have.

Andrew, does your carb have the choke coil on the side of the carb under a round black cover or does it have a rod that goes down to a well in the intake?

Here is a pic of the one off my 78, its partially apart and missing a thing or two.  The part highlighted in red is the part I think we are talking about.  The choke is the black thing inbetween the brakes.  In 75 the cads started using the electric choke like the one in the picture.  I think the 74's used one that looked the same except for it didnt have the electrical connection and had a tube that ran into it from the manifold. As far as I know the 68-73's had the choke coil in a well in the intake manifold and a rod that goes up to the carb.

It has the choke rod that goes down into the well.  I had a 67 Eldo that I had to convert to a newer electric choke, because the manifold was so full of crap that it would make the car idle rich, fouling the plugs.  When I get I a chance, I'll post a photo.  I think the a/c idle speed-up is on the other side of the carb.

Thanks for the thoughtful comments!

[Tom Hitchcock]

Andrew:  This post may be a bit stale, but I've only now had a chance to examine my '68 CdV and can confirm the second vacuum line, to the carb's rear, is explained on page 6-73/74, item 103, as the Air-Condition Idle Speed Up Control Adjustment. Its hose runs from the carb to the firewall where it enters the vacuum valve control head. This small diameter hose should also be color-coded.  Figure 6-99 in the Shop Manual has a pretty good side elevation drawing of this device and adjacent fittings.