Sorry this is so long.......

Ok, so here is the back story. I'm working on my 86 D100 pickup, stock 318/auto, 2bbl. This truck had the Electronic Spark Control computer mounted under the fender, behind the battery. I'm not sure if this computer qualifies as a lean burn or not, but all it really did was control spark timing. As with the lean burn mounted to the air cleaners of the cars, the "vacuum advance" was attached to the computer. Now I've been told that this wasn't actually a vacuum advance, but more of a map sensor. Whatever it was, when I plugged in the vacuum hose, the timing changed. The hose, plugged into it's original location on the carb, did have full time vacuum.

Well, I eliminated the computer system by swapping in a "ready-to-run" distributor I got off ebay. It's one of those dist. with the built in modules. All I needed to hook it up is a power wire to the coil and two wires from the coil to the dist.

I've gotta say, this was probably the best thing I've done on the truck so far. It runs so much smoother. The only thing is, I'm not sure how to hook up the vacuum advance. It's my understanding that the advance should be hooked up to ported vacuum, not full time vacuum. But the original "advance" was hooked up to full time.

I only have two vacuum ports on my stock Holley (Carter BBD designed, Holley built) 2 barrel carb. One port was hooked to the original advance, the other port connects to a thermal-vacuum switch, which then connects to the EGR. But this port does not seem to have any vacuum at the carb, even when I open the throttle. Does it have vacuum when under a load?

I guess my question is, should I leave the vacuum advance disconnected? Should I hook it up to the full time vacuum? Should I hook it up to the other vacuum port and leave the EGR disconnected? What would be best for the best fuel milage and throttle response? Right now, I'm driving the truck about 150 miles a day on the highway and I'm getting about 14 mpg. I'd like to do better if I could.

Also, my throttle rsponse, although not entirely perfect, seemed to be better with this new distributor than it was with the old computer. I have been driving it with the vacuum disconnected for about a month (the 14 mpg was with the vacuum disconnected) and throttle response has been fairly good. I like to step on the gas and go, not stumble around coughing and wheezing. Out of curiousity I guess, I hooked up the advance to the full time vacuum. I don't know if there is any improvement in milage yet, but throttle response, especially when cold, sucked. My initial timing is set about 9 degrees. I have no idea where it's at with the vacuum connected. I don't have a timing light (borrowed one for intitial settings, can't do that now). Anybody have any advice at all?

One last thing, the carb is NOT a feedback carb. Just because I originally had a computer does not mean I had a feedback carb. There are no wires going to this carb other than for the idle solenoid. Also, swapping this carb for anything else is out of the question. Yes, I would love to swap in a four barrel on an eddy manifold, but I have no money. Even swapping this carb for an older version is out because, again, I have no money. I just want to know what my best option is: leave the advance disconnected, connect it to the full time vacuum, or connect it to the other port. And what would be the effects of each option?

Thanks...

Really? Nobody knows anything about vacuum advance?

I'm just wondering if I should leave it disconnected and run no vacuum advance at all, connect it to the full time vacuum port, or to the port for the EGR. What are the pro's and con's of each choice?

Its supposed to be hooked up to a ported vacuum source....meaning no vacuum at idle. Do not hook it up to manifold vacuum. You will have to hook it up, as it will give you much better fuel economy, driveability, and quite an increas in part throttle performance.

The distributor MUST be hooked up to the Ported-Vacuum source on the carburetor. If you hooked it up to any common Manifold-Vacuum source, the "Vacuum-Advance" would be "Advanced" all the time.

The "Ported" vacuum source on the carburetor is at Zero when the engine is idling.

Ok. But if you read my initial post, my carb only has two ports: one is full time vacuum, the other is connected to the EGR through a thermalvacuum switch. It seems this port actually doesn't have any vacuum at all as there is nothing at idle, but also nothing when I rev it up. Maybe it only works when under a load? If neither of these are going to work for me, would it be better to have full time vacuum or no vacuum at all?

Thanks for answering

A: In short, "no vacuum at all" would be better.

Do you still have the instructions for your carburetor, or could you go online and get some information about your carburetor?

There should be information about where the Ported-Vacuum port is located on that carb.

If it were a Holley, you could use their website, but it's not.

On my '71 Charger, I don't use Vacuum-Advance (mechanism removed) but my Charger isn't a daily-driver and fuel-economy is not an issue.

In any event, for it to function properly, you need a "ported-vacuum" source.

You might want to check this recent post out if you can spare the time:

This is a Good Moparts Post for you to Review

I have no "instructions" for the carb. It's the stock carb for this application as supplied by Dodge. Although it is built by Holley and says Holley on the body, it's basic design is the same as the Carter BBd that Chrysler has used on the 318 since the dawn of time.

As I've said, the only ports on this carb is the full time port, to which the original "vacuum advance" on the computer was connected; and the other port for the EGR. Would you recommend that I disconnect the EGR (which was actually disconnected when I bought the truck years ago) and connect my advance to that port?

Or is my only option to buy a reman carb for an older model to get a ported vacuum port? I don't have the money to do that, and I'm sick of throwing money at this engine that I should be using for parts to swap my 440 in.

I have the same carb on my 84 and as you said there is know "ported" vacuum as we have come to call it. The port where it apears to have no vacuum actually dose but only about 2.5" max. that wont work the vacuum advance.I have a vacuum amplifier that I am going to try and see if it will work but haven't got there yet.
If I were you I would leave the vacuum disconected and advance the timming untill it just starts to spark knock under load then back it off just untill the knock goes away. I did that with mine and my dist has a light spring and no heavy spring. Mechanical advance all in by 1800rpm I have it set for 34* total and that comes in at about 20* at idle. I get 15-16 mpg. I would guess about an extra 1-2mpg if I could get the vacuum working.
By the way when you get your 440 in don't even check your millage.

Well like was said already, you need a ported vacuum source. But if I were you I would try hooking it up to a full-time vacuum source. Only difference between ported and full vacuum is the ported vacuum will give no vacuum at idle and less vacuum at lower throttle levels. If you hook it up to full vacuum, at worst you'll get a high idle speed and it may want to ping or stumble at tip-in. But with your base timing set at only 9*, I would give it a try.

Like I said jut keep advancing it untill you get spark knock under load then back it of just a little until the spark knock goes away. You can do it without a timing lite. 34-36* total is just a referance point. every engine is diffrent and I usually end up tuneing it by ear. I use a timing lite to get it close because I have one but i've done lots without one also. I will hold the rpms at 2500-3000 and adjust the dist untill it starts to change tone or labor a little then I back it off a little untill it is smooth the test drive and check for spark knock. Just do it you won't hurt anything. If you have a spring kit for the mechanical advance try to set it for full advance at your normal cruise rpm's mine is like 2200 at 60 with 235/75/15 tires and 2.94 gear.