Disty Vacuum

[drddan]

What is the best place to hook the vacuum from the disty, to the manifold/carb?

I have a Weber 32/36 DFEV.

[georgeb]

Advance biscuits need to be hooked to the carb above the throttle plate

[BigElCat]

Your 32/36 DFEV should have only one vacuum take-off tube. Use that tube. It ports in above the throttle plate.

Connect it to the large vacuum can on the dizzy. Leave the tube on the small can open....no hose...no cap.

I'll try to scan the FSM diagram regarding the vacuum advance on the B3 dizzy.

[BigElCat]

Had to install the scanner on the new PC.

Now....can I upload a 410KB PDF?

No. I have to scale it down or zip it.

This is the definitive answer to this question. I was only half right before.

[BigElCat]

:wav:

I can read it! Finally and for the first time. Converted to jpg and ran it thru Irfan View.

Answer:

Run a vacuum line from the Weber vacuum tube to the large can on the dizzy.

Run a vacuum line from the small can on the dizzy to one of the vacuum ports on the intake manifold directly below your Weber adapter.

I'll link us to your pic of your intake.



Any of these vac tubes can be connected to the small can on the dizzy. I'd use the T on the lower right. Cap the rest. Your vacuum/mechanical advance curve will be like Mazda intended. I bet it will work great for the Weber.

[drddan]

Cool beans!!!! :p

I was baseing vac hookup like it was on the factory setup.
I knew it wasnt right for the present setup. The old setup had the large vac line going to that maze of vac tubes under the intake, that is no longer there, and the small tube going to top of intake under carb.
They are now both hooked to top of intake under carb, using the T port and the rearward port next to it. Figured i'd deal with getting them right later (later is here, now)

It has other issues, and are in my swap thread

Thanks a bunch!!!

Still working out the bugs, but it's gonna be awesome when I do.

[zoe60]

Hey Doc. Where do you run your vacuum advance from? I used to have mine hooked up like original, but my idle was erratic. Best results I've had are coming out of the port on the carb under the choke. I teed the line and fed it to both ports on the distributor. Idle is much more consistent, and mileage went up slightly. Some people think that one port on the disty retards timing and the other advances it. I've applied vacuum to each port and found that to be false. They add up and give you advance. You may already know all that but it took me some experimenting to figure it out. Hope it helps.


This is from your garage thread. Trust me, it works the best.

[BigElCat]

Best results I've had are coming out of the port on the carb under the choke. I teed the line and fed it to both ports on the distributor. Idle is much more consistent, and mileage went up slightly.

Zoe...I can't argue with your results, the effect it had on the way your engine runs. But I can say for certain that what you've done is decreased the vacuum advance. The small can on the distributor does pull the stator in the opposite direction as the big can. It doesn't "retard it" per say, it limits the amount of the advance.

IMHO...you should try hooking the small can to the intake manifold, and leave the big can hooked to the carb.

[Movin]

?? Using a timing light the big can gave 14 degrees. The little can gave 10 degrees.
They added together for 24 degrees. The computer adds the rest.

[TominMO]

?? Using a timing light the big can gave 14 degrees. The little can gave 10 degrees.
They added together for 24 degrees. The computer adds the rest.

But of course that wouldn't apply with the Weber; no computer hookup since all that stuff was removed. Captain Obvious here.

[Movin]

Exactly , and on top of that some one was saying to only use the inner
can. Another mentioned that some believe one can retards timing. At
4100 feet we need all the timing we can get.
Perhaps watching the can hooked to intake vacuum fall as you step on it
has led to this retard thing. I would suspect that both cans hooked to
ported or above plate vacuum would produce the best results even at low
altitude.

[zoe60]

?? Using a timing light the big can gave 14 degrees. The little can gave 10 degrees.
They added together for 24 degrees. The computer adds the rest.

That's how it works, I don't care what anyone says. I tested it myself with a timing light and a vacuum source. Plus, when I teed the two together my gas mileage went up almost 1 MPG. I don't think the computer has one thing to do with it. Do what you want. Bet mine will outrun anyone's with the same engine and carb. Movin- You always seem to know what you are talking about. You don't just talk out your butt like some people. You actually researched it like I did in this case. Sorry, My computer won't add advance because I have an aftermarket ignition and the 3rd wire on my disty is unhooked.

[Movin]

Thanks Zoe, I am here to share what I know, learn what I don't
and have fun while here, this is a great crowd with an incredible
amount of knowledge in a lot of area's!

[dliverance]

SO what was the verdict on this? I'm running dual dcoe carbs on my car and I do not have pre throttle plate vacuum reference. I'm guessing from this that ideally, I would want the large can connected to vacuum before the butterfly and the small can connected to manifold vacuum.

can I get away with running both to manifold vac?

[dliverance]

If I were to take a guess at it, the large can operates at idle because vacuum is present with the throttle closed. This creates 24* advance at idle. With partial throttle, the manifold vacuum goes away and instead is present before the throttle body. The small can is connected there and would produce a total of 20* advance for highway driving with partial throttle. I'm also going to guess that our distributors have a dual diaphragm because there's no centrifugal advance and it just uses the small can for partial throttle driving instead.

If I'm wrong please correct me. I've been racking my head all night trying to figure this out.