Reed you hit the nail on the head again. Now this may start a argument with the white beards, it was common practice for hot rodder's to connect the vacuum advance to ported vacuum to make up for the lack of total mechanical advance of a dizzy. If your vacuum advance adds timing from vacuum, connect it to strait vacuum. Use a port by itself if you can , one that is not influenced by other things. The whole point of vacuum advance is to provide advance to compensate for intake reversion (exhaust gasses contaminating the intake charge during valve overlap at lower engine speeds IE idle or cruise) If you move your vacuum port you may find your idle speed to high, disconnect your vac advance and re time the dizzy. Get the throttle plate back on the idle circuit.
Vacuum for advance is in correct port and it is in the idle circuit. I think Reed may be correct that I got one with a governor for the idle circuit. I can move it a little either way. It sits right in the center of that spot. I was unaware they had a governor in the idle circuit. Seems stupid to me but that's the government for ya. May work on paper but in the real world it doesn't.
I am not an advocate of hooking up stock Chrysler distributors to manifold vacuum advance. The distributor and ignition system is designed to operate off of a ported vacuum source, not a full-time manifold vacuum source. Running manifold vacuum advance requires you to change your base timing which then requires you to change your idle speed and mixture settings. It also reduces the overall timing advance the motor will see because the base timing will be significantly retarded from where it should be. It is a bad idea. There are other ignition system designs that are designed to use manifold vacuum, or even a combination of manifold and ported vacuum. The Chrysler system doesn't.
Something isn't right if you can only turn the idle mixture screw a little bit. The governor I am talking about is a small diameter orifice in the tube of the idle circuit. It is not a physical limiter on the mixture screw. Does the mixture screw have one of those big plastic caps on the end of it with with a big "+" on the end? That IS a mixture screw limiting cap, and it can be removed. If it does have a plastic cap on the mixture screw, the cap can be removed and the screw should then be fully adjustable.
The idle mixture screw doesn't have a cap on it. It actually doesn't stick out past the base itself. It's a cap style screw that requires an hex key. I've seen this style used before on carbs. I have longer idle screws around, not that the length matters but could the end pitch be different enough to effect it? When I get the time I'll look at the idle circuit an see what it looks like. It may be a few days till I can pull it off. Is that tube able to be drilled out to open it up or is it stuck as it is?
I can't recall offhand if the limiter can be drilled out. It has been a while since I opened one of those up. I assume it could, but I would resort to drilling anything as my last step.
How much movement do you have on the idle mix screw? is it possible that the concealment plug was not removed enough to let the mixture screw come out? The factory installed a plug over the mixture screw when the carb was new and any remanufacturing would requires the drilling or grinding out of that plug and the metal around it. Is it possible that whoever removed the concealment plug left too much of the surrounding metal in place to allow the idle mix screw to be adjusted?
I just want to make sure we are understanding each other on the screw as I don't think I explained it right. Could be me that's not completely understanding you too. My fault, no worries. I can physically move the screw as much as I want in and out. I can remove it completely if need be. The limited movement I mean is in adjustment of flow. If I move it much in either direction the engine starts to stumble from being out of adjustment. The screw is set at about 1 1/4 to 1 1/2 turns out. Maybe it's right where it needs to be, I don't know what is normal for these carbs. I know it varies based on altitude, weather, engine, etc... Right now with the adjustments I made with the choke and timing I have it running pretty good at the moment. Twice scence it's run a little rough. I don't know how to explain it in words. I start it and it will run rough at idle. At higher idle it runs fine. Runs like that till I shut it off. But then later I will start it and all is good. I hope this helps and it's hard to explain things properly when not in person. I'm not looking for perfection here, it's an old engine with some miles. I know it's not gonna run like new. I'm just trying to figure out why it acts up at times with this carb. Thanks again for your input.
Oh! OK, I misunderstood your post about movement on the screw. Sorry, my fault.
The internal mixture limiter prevented the idle mix screw from going beyond a certain level of enrichment. The mix screw could make the mix leaner, but it could only richen it to a certain point.
The engine running rougher if the screw is turned in or out past a certain point is normal. One way the mix is too lean, the other way the mix is too rich. If it starts to stumble if you turn the screw out past a certain point, then you don't have a limiter in the idle circuit. 1 1/4 - 1 1/2 turns out is withing the range of normal. For now, set the idle mixture for maximum vacuum at normal idle speed with the engine fully warmed up.
If you have the money and are tired of farting around with unknown quality rebuilds, here is a true, NOS, never used Holley 1945 on ebay that would work good on your van:
I dug around in my garage and found that I have FOUR 1945 carbs. Unfortunately, none of them are suitable for your use.
I had another thought- the 1945 carburetor was used from the mid 70s to the late 80s on the slant six. This meant that the carb was introduced when the only computer in the engine bay was the ignition conytrol unit but lasted until the days of computerized EFI and computer controlled transmissions. This carb was used duting the time when Chrysler was introducing the "lean-burn" engine control systems, and 1945 carbs were made for lean burn systems where the lean burn computer controlled the timing BUT NOT the carb! This is important because the carburetors used on timing-control-only lean burn systems look externally exactly like an older 1945 carb, but have some important differences that would not be noticed by nearly all commercial rebuilders of carbs.
The main difference I am talking about, and the difference I think might be causing your problem, is the difference in the vacuum signal for the distributor vacuum advance. 1945 carbs built for use in lean burn systems where the computer controlled only the ignition have all the same exterior vacuum ports in all the same positions as the older non-computer related 1945s, but the carbs built for use with a lean burn system give full manifold vacuum at the vacuum advance port all the time instead of no vacuum at idle and full vacuum off idle. The main difference was the port for the vacuum signal on the non computer carbs was above the throttle plate at idle but the port was below the throttle plate at idle on the computer related carbs.
Here are some pictures to explain. These pictures ae of two 1945 carbs. One is a late model carb where the carb was not computer controlled but it was designed for use with a computer that controlled the ignition system. The other is an older 1945 that is designed for use with a fully mechanically controlled distributor that uses trafitional vacuum advance. The pictures are taken with the carbs upside down and the throttles fully closed, except the third picture where the throttle on the old 1945 is slightly open.
The first picture is of a late 1945 carb that was intended for use with a lean burn system. You can clearly see the idle mixture screw port, the transfer slot, and the vacuum advance port in the throat of the carb. All of these are clearly below the throttle plate at idle and therefore receiving full manifold vacuum. This carb was intended to be used with a lean burn computer that required full manifold vacuum at all times to control the vacuum advance.
The second two pictures are of the older carb. You can see all the same landmarks in the pictures, but the main difference is that the vacuum advance signal is ABOVE the throttle plate so it has a vacuum signal only AFTER the throttle is opened beyond curb idle. The vacuum port on this carb is a thin rectangle rather than a round hole, but it is in the same place as the late 1945, just above the throttle plate.
Why does this matter? I suspect you may have a situation where the distributor vacuum advance port is seeing a vacuum signal at all times because it was intended for use with a lean burn system and not with a vacuum advance distributor.
Try unplugging the vacuum advance hose from the carb and capping the fitting on the carb. See if that changes how the engine runs. If my suspicion is correct, then your cold running problem will improve.
That's a lot of info right there. Thanks. I will have to look at the carb itself to see how the slots are. I know when at idle I am getting no vac at the distributor. But I will double and triple check that with a guage. My van originally came with the lean burn box of crap that only controlled the timing and not the carb. I should have kept it but I have a habit of throwing stuff out that I don't use after a bit. I'll check it with a guage today and get back to ya.