Single or Dual?



What distributor (DSII) should I get - single or dual vacuum advance?

After reading Chilton and Haynes manuals, it sounds like the dual vac. advance is a pretty efficient system for the best in driveability. Is this correct?
I think most are going to say SINGLE, when it comes time I will do single also. If for no other reason then I only need 1 vacuum line to the dizzy. There are some others on here that use the single but unhook the vacuum advance. I guess the part I would wonder about is if you change carbs (larger or smaller) does your vacuum readings on the ported/manifold stay in the same relation to what the original was designed to work with?

ack, 1 vote for Single

Well I would be using a stock Fairmont carb in conjunction with it. One line or two lines, that doesn't bother me.

The thing that sounds good about the dual is the advance/retard function. The manual says it allows for a more complete combustion.

Which engine do you have (casting # on side of block below exhaust manifold would helpful). What carb and dizzy are you using now? Why do you want to go electronic? What is you longer range plan for the car? The choice of dual / single vac advance should be viewed in the light of your vision for the car.

If you just want to go electronic (happy with current carb / dizzy performance) you can go electronic for very little money via Pertronix. If you want a performance dizzy to go with a later carb upgrade it would be wise to make a dizzy change. There are two upgrade choices if you go this route. What you don't want to do is invest in something now that won't work for you later. No reason to do the job twice.
OK, here goes....

The block and head are both from a '78 Fairmont. The mechanic who rebuilt it put the Loadomatic distributor in and made an adaptor to use the 1100. I used that awhile, then installed a Holley 1946, which is what came on the Fairmont. I used this for about 1 1/2 years with the Loadomatic distributor and had no problems at all, despite what people say about them not working well w/other carbs. Well, about a month ago, I switched back to the 1100 because of choke and idle problems with the 1946. I currently have a Pertronix unit installed in the Loadomatic.

Since I've had the 1100 on it again, I have noticed "flat spots" - I guess you would call them - when you stomp the accelerator. According to Pony Carbs. this is common with the 1100. They claim that they fix it in their rebuild, but I really don't want to take a chance and spend $250-300 just to possibly have it do the same thing.

So...I have decided to go back to a 1.75 carb (haven't decided for sure which one), and I would like to get the right distributor to match. The car will be a daily driver when finished. It's not built for performance, but for driveability, rather. Gas mileage is a factor, also.
i had the same thing.....

my car came with a holly and i got a autolight 1100 off ebay and it had flat spots in it just like yours. I changed carbs because i was having choke problems with the holly. which i still am or at least i think....i just got done re-building my engine
You can stay with the 1946. Check your local parts store for rebuilt carb. Pony also sells the 1946 for the same price as the 1100, $180 exchange. I wouldn't put the 1.5" carb back on the 1.75" manifold.

If you upgrade the carb you will need to change the distributor. You may be able to retain the Ignitor II if the replacement dizzy has the same shaft. The Loadomatic typically had a "D" shaped rotor drive. If you can't find a dual advance (Mechanical / Vac) distributor (68 - 73) with this drive you will have to acquire a new Pertronix setup. You can avoid this risk by staying with the 1946. If you are looking for mileage this is probably the better way to go.

If you elect to upgrade I would look into the Stovebolt Holley 5200 ($65 rebuilt), use a Clifford adapter ($60 as I recall) and switch to the dual advance dizzy ($65 rebuilt). A good used motorcraft 2100 can be had for the same price (use the 1.08), and Clifford has an adapter - same price. With either of these you will need to do a little shade tree engineering to get the throttle linkage converted to run these carbs, buy its not a difficult job.

Good luck with you project
I currently have the 1100 on there. I don't think there's a problem with adapting it to the 1.75" intake. With a properly made adaptor, it should work fine. I used it that way a long time before I switched to the 1946 (which I do not like).

The only thing that really made me think about switching back to a larger carb is the flat spots that the 1100 has. But, in the light of the good info. I received about Pony Carbs, I have decided to get it rebuilt by them. IF that doesn't fix the problem, then I'll probably go back (reluctantly) to a larger carb and DSII.