The Stovebolt Site Forums The Shop Area Engine Shop Carter Carb Vacuum Confusion

Hi Everyone,

I've got a vacuum port question. But first the particulars... The engine is a 235 built in 1959 and equipped with hydraulic lifters. It was originally hooked to a castiron powerglide transmission. The engine is currently not installed in my truck. I hope to do a swap between the currently installed, nonfunctional engine and this one sometime this spring/summer. Although not installed, it does run while sitting on my engine stand. The engine came to me with a Rochester 1 barrel. After reading lots of posts about the pros and cons of Rochester carbs, I decided I'd look for a Carter and give it a try. So I found a Carter 3211S, which is supposed to be an aftermarket carb designed for my vintage of 235 engine and I bought it.

I also read a lot about whether these had vacuum ports or if you needed to use the manifold vacuum port for the distributor advance. I thought that the consensus was that these carbs did not have the distributor vacuum ports on the base. This carb has 2 openings on the base, one of which is threaded, one of which is plugged. Here is a pic of the Carter 3211s base with threaded opening . Here is a pic of the inside of the base with 2 openings visible. One is horizontal and one is vertical with the horizontal opening is just to the right of the vertical opening in the pic. When the bottom butterfly is closed, the openings are below the bottom butterfly. In the first pic, you can see 1 opening and 1 plug. I haven't touched the plug, but it clearly is an opening from the outside to the other opening inside the carb.

The question is: are these vacuum ports for use in operating the distributor advance? If not, what are they for and should I be using them or plugging them?

Here's a closeup of carb model numbers to show the 3211s and the number of the base.

Here's a closeup of underside of the base showing all of the openings.

Here's a different view of the openings showing the plug and threaded opening.


Thanks for looking!

The stovebolt 6 cyls. used ported vacuum for the dist. advance. One of the openings might be ported vacuum & the other manifold vacuum. You can follow the passages to tell. The manifold vacuum will enter below the throttle plates & the ported will be above. Or with the engine running the manifold outlet will have vacuum at idle & the ported will have vacuum only on part throttle.

Wrenchbender,

Thanks for the reply. Based on your description, both openings are for manifold vacuum, as they are both below the throttle plate. Here is a better view of the openings . It is easier to see in that pic than the original pic I posted.

Interestingly enough, I looked at the original Rochester carb and found that the distributor vacuum connection was also manifold vacuum. Here is a series of photos showing the original Rochester carb, a closeup of the vacuum connection point and the inside of the carb base showing the vacuum openings. The last pic is a little hard to see the 4 holes, but they are in the pic and just below throttle plate. Of course, the carb is upside down for picture taking, so the openings appear to be above the throttle plate, but are really below it.

I can't make much from your photos but a model B Roch. has the dist vacuum outlet on ported vacuum. It is above the throttle vales. I just imagine the Carter is the same on at least one of those outlets. When you get it running, test each outlet for vacuum at idle or vacuum at part throttle only. You can experiment & find which one works best for your engine.