Spark Control Valve on 1100



I need this answered for me: do you plug it or not when using the '68-73 dual advance distributor? I was reading through the archives and saw one person saying to plug it and another saying to put a fitting there and use it as your vacuum source.

Which do you do?

If you plug it, do you use the original vacuum source on the carb. or vacuum from the intake manifold?

I am confused. :|
Howdy hsfd202:
The Spark control valve is basically a vacuum switch. If you don't at least plug it you will have an intermitent vacuum leak. If your remove it and replace it with a vacuum fitting you will have a ported vacuum source. Or you can plug it and use a full manifold vacuum source, either at the base of the carb or the intake manifold. Your choice.

All FoMoCo carbs are designed to use ported vacuum with several mitigating switches. So you have to experiment with what you have to see what works best.

Adios, David
I do believe that the spark control valve was used to switch between the ported, and the manifold vacuum, based on engine load. This worked in combination with the Loadomatic, or Dual Vacuum distributor. Based on engine load the spark control valve will either supply ported vacuum via the ported vacuum outlet (which is lightly above and to the right of the SCV on the carb) to the retard diaphram on the distributor, or manifold vacuum via the mainofld port to the advance diaphram on the distributor. Inside these distributors are no advance mechanism at all. The advance, and retard of the timing is accomplished soley by engine vacuum. If you choose to use the later dual advance distributor, you will need to plug the spark control valve completely by purchasing a brass plug. You can then connect the vaccum advance to either the ported vacuum on the carb, or plug that up as well, and connect directly to manifold vacuum source (try both and stay with the one that produces the best result.) I just went through this myself.
Good Luck, and let us know how it goes,


As time allows I will try to get some pics of this available.
I hope this doesn't sound dumb, but how, exactly, will I know which is better? What do I look for?

So, the place where the s.c.v. is located would provide ported vacuum. And the place where the stock vacuum line hooks to on the carb. would be full manifold vacuum. Correct?
Both places on the carb, either in the port that houses the scv, and the vacuum port on the carb provide Ported vacuum. The only place you will get manifold vacuum from is either the carb spacer, or the manifold itself.

Just prior to removing the load-o-matic, I had installed a brand spankin new spark control valve. The funny thing, regardless of engine speed, the advance never changed. I think that you all have been lied to all these years. I think that the SCV is there to maintain the advance at a certain point, and let it progress no further so that you ....

But seriously.

Anybody out there know the threads on the SCV so I can properly plug it. They look pretty fine to me.
Ok, here's a picture of an 1100 for a '68 200...

Neither vacuum hole looks plugged, so where did Ford hook the vacuum line to? The old s.c.v. location or in the original location on that side?
I will try to post a pic tomorrow of my 1100. If you look closely at the SCV port you will notice no threads. The hole is still there, but blocked off in the casting. The ported vacuum port is still available if you so choose, but no longer controlled by the SCV.

The Manual has a very good section on the 1100. The Spark Control circuit is shown in a cut away view, so you can follow the routing of where the source to the vacuum advance comes from. The SCV acts more like a dampener. The actual source of the vacuum is a combination of Ported and Manifold.

As far as the picture provided by hsfd202 the SCV is threaded into place in the large opening and a nipple is pressed into place in the smaller.

I agree with Bill, if you are going to use the later distributor the only vacuum available for advance would be from the manifold.

Good luck, Ric.