4988S has no ported vacuum?

[Riv]

Hi everyone -

Last fall I picked up a nicely rebuilt quadrate for my '69 Firebird.  I was told at the time that the carb had been dialed in and to be honest I have no complaints at all about the build.

However, after mounting it to the intake I noticed that this particular carb - apparently a service replacement - has less vacuum ports than I'm used to seeing.  There was one on the back for the brake booster, but the only other one is higher up on the passenger side in front, which I believe is manifold vacuum.

I currently have the distributor advance run off of the manifold vacuum.  Everything seems to be running great, but I'm not sure what I should do.  Is it strange that there would be no ported vacuum?  Should I have a port added to this carb?  Do I even need one? 

I'm not sure how to proceed.  Any thoughts?

Thanks!

Tim

[Kenth]

Carter 4988S is an aftermarket Quadrajet for 1970 Pontiac V8. (Genuine Service Replacement units were made by Rochester.)
1970-74 Pontiac (except 1971 455HO) uses the TCS-system to control the ignition vacuum advance, thus no ported vacuum source on your carb.
Most pre-emissions engines used full manifold vacuum and if engine runs fine with full manifold vacuum to the ign. vacuum advance i would just leave it there.
If needed a ported vacuum source can be added.

HTH

[Cliff Ruggles]

You will not find adding ported advance easy, but it can be done.

As mentioned if it works OK with MVA I'd just leave it that way.

To add ported VA you MUST have the source location at precisely the correct location above the throttle plates.  This insures that you get FULL MANIFOLD VACUUM to the distributor with the slightest movement of the throttle off idle.

At that point the ONLY difference between a manifold and ported source to the distributor is no vacuum idle and coasting with the ported source.

Distributor vacuum advance is a very misunderstood topic, even by some very knowledgeable folks who claim to know that deal. 

Tread softly in that area and don't think for one second that ALL of these engines will run better with manifold vacuum to the advance. 

Here I use what works best for the engine combination and more times than not if I had anything to do with the engine build it's not going to want, need, like, or respond well to running the timing clear off the scale at idle speed......FWIW......Cliff