Greetings. So the lean burn computer burned out on my 84 B150.

I converted it to a GM HEI 4 pin module and it ran OK but I had no advance. Lack of power.

Bought an HEI distributor and it runs better but cannot find any ports for the vaccum advance on the one barrel carburetor that is not before the throttle plate. Advance kicks in at idle.

Where can I take a vacuum signal that is not manifold vaccum?

There are two 1/2" ports above the throttle plate.

One goes to the PVC valve. Can I tap in here?

Video if my conversion:

https://youtu.be/EC0v_tOHEwc

I am not sure what you mean by an "HEI distrubutor. Hopefully you mean a standard electronic ignition Chrysler distributor and not one of those unit on the market that actually has a Chevy distributor head grafted onto a distributor body that will fit in a slant six.


Bad news. Carburetors that were built for lean burn ignition systems do not have a vacuum port that will work correctly with a Chrysler electronic ignition distributor. The lean burn systems use full manifold vacuum as the reference source for timing advance. Older standard electronic ignition system (madae by Chrysler) use a ported vacuum source that has no vacuum when the throttle is closed. A lean burn carb does not have a vacuum port that has no vacuum at idle but full vacuum when the throttle is opened. Short answer is that you will need to find an older carburetor from a non-lean burn vehicle.

Ported vacuum = Manifold vacuum everywhere except at idle.
Vacuum advance at idle is not necessarily a bad thing. If the cam in the motor has a lot of overlap or the stock motor gets a lot of egr at idle, using manifold vacuum to bring in vacuum advance at idle can really help to smooth out the motor at idle. As soon as you step on the throttle and open the throttle plate the manifold vacuum equals ported vacuum.

You mention that you have two ports above the throttle plate on the carb that you have, those will be ported vacuum that do not have vacuum at idle. And I thought that the PVC connection to the carb was always below the throttle plate.

Nice job on the video. For the HEI modules, I also went through a couple of modules, then I paid extra for the Genuine AC Delco module and it has been fine. I bet that if you get a used OE module out of a pull a part it would be old, but good.

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https://www.youtube.com/watch?v=uX8Nj8ABEI8

Sorta, yeah, but the onset curve is different, too. It's not just a single binary difference between no vacuum at idle and yes vacuum at idle.
True; vacuum advance at idle can be useful in a few very specific situations, mostly related to getting at least marginally adequate driveability with crude emission controls of the mid-1970s; here's what Chrysler had to say on the subject in 1976 (remember, statements in this document are in context of engines that were strangled, starved, and retarded to squeak past their new-vehicle emissions type-approval tests so they were legal to put on the market; these statements do not necessarily apply to vehicles not in that situation):





On a stock or stock-ish engine tuned to run well, vacuum advance at idle often does the opposite of helping (see here for a case study).
EGR valves are all and always closed at idle. The only Slant-6 engines that would get EGR at idle are those in California-spec '72 cars, which had a "floor jet": a plug with a hole in it, screwed into the floor of the intake manifold plenum so exhaust would (always) flow in from the exhaust manifold. There was no valve or other means of modulation or shutoff. These cars had an extra-high idle speed spec and still ran poorly for the obvious reason.
Not necessarily. That carb will have a venturi vacuum port about halfway up the carb body. It is not suitable or capable to operate the vacuum advance.
That's correct, it always is. And teeing the distributor advance into the PCV would be very much the wrong thing to do.

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So... for education sake, what model carb would an '84 B150 have been equipped with? And what model carb should a guy want to install to have ported vacuum and good idle characteristics?

Thanks. Neil

A Holley Model 1945 Type R40088, R40089, R40102, R40103, R40159, R40160, or R40244 (non-feedback, no O2 sensor screwed into the rear wall of the central collector of the exhaust manifold)

or

A Holley Model 6145 Type R40097, R40098, R40099, R40161, or R40162 (feedback, with O2 sensor).

Which of these models and types would have come on your particular vehicle would depend on its transmission, emissions control package, intended market, and production date.
Answer depends on the rest of the vehicle. How well do you want it to run, what's the budget (in money, time, and effort) for this round of upgrades, will you be keeping the van's catalytic converter/s (replacing them if they're clogged, as they very well might be)? Do you have to pass any kind of inspection or emissions test with this vehicle?

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Too many people who were born on third base actually believe they've hit a triple.

Sorry guys for the late reply.

I am not sure what you mean by an "HEI distributor. Hopefully you mean a standard electronic ignition Chrysler distributor and not one of those unit on the market that actually has a Chevy distributor head grafted onto a distributor body that will fit in a slant six.

Not quite. I just mounted an HEI module and mounting pad on the firewall. Watch my video.

I know the one your talking about. The distributor I used was the one Chrysler issued as a replacement for the Lean burn system. It's got weights inside it and a vaccum advance. I did not use an actual Chrysler control box but a GM 4 pin HEI module. I thought Chrysler called these an HEI anyway.


Bad news. Carburetors that were built for lean burn ignition systems do not have a vacuum port that will work correctly with a Chrysler electronic ignition distributor. The lean burn systems use full manifold vacuum as the reference source for timing advance. Older standard electronic ignition system (madae by Chrysler) use a ported vacuum source that has no vacuum when the throttle is closed. A lean burn carb does not have a vacuum port that has no vacuum at idle but full vacuum when the throttle is opened. Short answer is that you will need to find an older carburetor from a non-lean burn vehicle.




I don't see why I couldn't knock out a Welch plug and drill and tap the hole for a fitting. I see a place for fitting on the right hand side of the carburetor. See my next post for a photo of my carburetor.
You'll have to click on the link.

Sorry I cant unload this photo until I shrink it down. So I've uploaded it to my Google Drive.

https://drive.google.com/file/d/1JTg45g ... sp=sharing

If you look at the port that the tubing is crooked looks like it's coming off the fuel bowl. There is another port about the same size hose on the other side.

If I disconnect either of these hoses, the engine idles fine. If I disconnect the hose on the right side of the carb, I can't feel any vacuum at idle but if I rev the engine, I can feel vacuum. I have not confirmed this with a vacuum guage but looks like the right hand port would be OK to tap into for a vacuum signal to my vacuum advance.

The hose connected to the crooked piece of tubing I cant feel any vaccum on this port.

Green dot is bowl vent

No apology needed, but please use the board's quote function rather than trying to home-bake it with bold-italic text.
I don't think this chronology is correct. AFAIK Chrysler didn't issue a non-Lean Burn distributor as a replacement for a Lean Burn distributor. The distributor you describe, with centrifugal advance and a vacuum advance, is…a non-Lean Burn electronic distributor.
No, Chrysler just called it "Electronic Ignition". HEI was GM's name. The HEI module is a better pick; you're on the right track there.

About a 99.8% surefire recipe for ruining things. That hole is not randomly sized, shaped, or placed; all three of those aspects are super crucial to how the engine runs. It's not something that can be guessed-and-goshed in the garage with a drill.
Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download. Head over there and get a nose into the materials relevant to the Holley 1945. If you're going to even consider the idea of making your own modifications, you really need to start by knowing what the carb's various ports are for.
If the engine won't idle well with the bowl vent hose connected (Matv91 has identified it for you) then there are problems that need to be found and fixed.
No.

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Too many people who were born on third base actually believe they've hit a triple.