34PICT-3 Vacuum Ports

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tandemtwins
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34PICT-3 Vacuum Ports

Post by tandemtwins » Sun Jan 05, 2020 7:12 am

I'm just starting to learn about "mechanical stuff"... and I've got what's probably a simple question. I just recently got ahold of an SVDA distributor for my 1973 VW Beetle, and replaced the 009 with it. (It was mainly a curiosity thing; I wanted to see how vacuum advance worked.) In diagrams I've seen, the vacuum hose from the SVDA attaches to the port on the left side of the carburetor (as looking at it from the back of the car). The vacuum port that is on the "rear" of the carburetor (pointing directly toward the rear of the car) is blocked off, unless one has a dual vacuum canister.

Today I watched a Youtube video on removing and replacing carburetors; this video showed the SVDA connected to the "retard" vacuum port, with the one on the left side of the card being blocked off.

Do these ports do the SAME thing? Is the vacuum produced by either the same, to where you could hook up an SVDA to either port, or are they different in their functions to where you should only use the port on the left side for an SVDA distributor?
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Rich McKay, Williston, FL
1973 Standard Beetle

kreemoweet
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Re: 34PICT-3 Vaccum Ports

Post by kreemoweet » Sun Jan 05, 2020 11:37 pm

The ports are quite different. You can actually trace the course of the vacuum circuits with just your eyeballs.
The left-side advance port is called 'ported vacuum', and leads to a small hole just above the throttle plate position
when it is closed all the way (as it should be at idle on a 34 PICT-3. It will thus have ZERO vacuum at idle. It will
jump up to a high vacuum level as soon as the throttle is opened a tad. Subsequently, it will have various levels
based on throttle position and volume of air passing thru carb, i.e. the load.

The port at the rear of the carb goes down to a largish opening at the very base of the carb, and will pretty much
be equal to intake manifold vacuum, which will vary from very high at idle, to low at wide-open acceleration, to
various intermediate values as the operating conditions change.

Your you-tuber had his hoses mixed up. The advance port is ALWAYS on the left side of the carb on all single-carb
SOLEX setups, although the vacuum circuits that lead to that port can be different on different carb models.

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asiab3
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Re: 34PICT-3 Vacuum Ports

Post by asiab3 » Mon Jan 06, 2020 2:15 am

kreemoweet wrote:
Sun Jan 05, 2020 11:37 pm
The advance port is ALWAYS on the left side of the carb on all single-carb
SOLEX setups, although the vacuum circuits that lead to that port can be different on different carb models.
To clarify, the H30/31 carburetors, though most of those are no longer made by Solex, have the SVDA vacuum port on the rear of the carb, and the SVA (vacuum only) port on the left side of the carb. All others that I know of follow this logic.

Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

tandemtwins
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Re: 34PICT-3 Vacuum Ports

Post by tandemtwins » Mon Jan 06, 2020 5:49 am

kreemoweet wrote:
Sun Jan 05, 2020 11:37 pm
Your you-tuber had his hoses mixed up. The advance port is ALWAYS on the left side of the carb on all single-carb
SOLEX setups, although the vacuum circuits that lead to that port can be different on different carb models.
Thanks, Kreemoweet, for your explanation. I found the video helpful, but was confused by the vacuum hose placement... being that on the "old" carb it was on the left and yet on the "new" one they hooked the hose up to the port on the rear. The video was produced by Mid America Motor Works; I thought they would have been a little more careful about "what goes where"!

The "infraction" occurs at 4:34 in the video.

https://youtu.be/34q8iVIbp_U
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Rich McKay, Williston, FL
1973 Standard Beetle

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Amskeptic
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Re: 34PICT-3 Vacuum Ports

Post by Amskeptic » Sun Jan 26, 2020 6:42 am

asiab3 wrote:
Mon Jan 06, 2020 2:15 am
kreemoweet wrote:
Sun Jan 05, 2020 11:37 pm
The advance port is ALWAYS on the left side of the carb on all single-carb
SOLEX setups, although the vacuum circuits that lead to that port can be different on different carb models.
To clarify, the H30/31 carburetors, though most of those are no longer made by Solex, have the SVDA vacuum port on the rear of the carb, and the SVA (vacuum only) port on the left side of the carb. All others that I know of follow this logic.

Robbie

Robbie, is there a place where I can go see this maddeningly cheap shot by those H30/31 tricksters?
Colin
BobD - 78 Bus . . . 112,660 miles
Chloe - 70 bus . . . 206,845 miles
Naranja - 77 Westy . . . 116,898 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 91 Lexus LS400 . . . 84,465 miles

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asiab3
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Re: 34PICT-3 Vacuum Ports

Post by asiab3 » Mon Jan 27, 2020 9:54 pm

Blue72Beetle showed me on his smoooth 72 beetle. I hooked up my vacuum gauge because I didn't believe him.

Solex h30/31 PICT ports:
left: vacuum-only distributor like our single port early bays.
rear, horizontal: vacuum retard for DVDA.
rear, angled up: vacuum advance for SVDA/DVDA.

Though it seems more universal as a replacement part, I don't think it's a cheap shot. Although terrible, the aftermarket is full of terrible 34 and 30 PICT carbs. I would rather have a genuine Solex h30/31 (jetted appropriately) than an EMPI clone of my personal carb……

My Mom's bug came with that Solex carb, and the ports worked the same way, until we found a 30pict3… ;)

Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

kreemoweet
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Re: 34PICT-3 Vacuum Ports

Post by kreemoweet » Mon Jan 27, 2020 11:54 pm

Here's some talk re the H30/31 rear angled vacuum port, with a nice picture showing the port in the carb bore
being pretty much the mirror image of the ported vacuum port in the 34 PICT-3/4 carbs:

https://www.thesamba.com/vw/forum/viewt ... sc&start=0

Do all H30/31 carbs have that port available? Or is it like the 34 PICT-3's, which all have the necessary channels
for that angled vacuum port cast/drilled in the body, but the final holes are drilled in only some of them?

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