Factory Dual Solex PDSIT Carburetor Adjustments

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Amskeptic
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Re: Factory Dual Solex PDSIT Carburetor Adjustments

Post by Amskeptic » Thu Mar 14, 2019 6:51 am

DannyZ wrote:
Wed Mar 13, 2019 6:33 pm
Wow, thanks for the quick feedback.
Danny, I was all stuck on the 1972 dual carbs with that one-year-only vacuum source off the right brake booster elbow.

You, however, remain stuck in vacuum hose limbo.

Do you know where the correct vacuum source nipple for the preheater thermostatic valve resides?
Diagram 2 shows it for the 1973-74 engines. It is on the central idling plumbing under the air filter, it is a little vacuum nipple next to the big pipe (blocked off) that used to go to the air pump.
Is it capped? Is it welded shut? Is it just open and sucking in air god forbid?
It is your vacuum source so you can do the mixture reference test!

I need to know how this missed your attention so I can redo the write-up and diagram.

The nipple off the right carb only has a little vacuum at mid-throttle for the now blocked-off EGR valves! thus, the nipple needs to be blocked off!)
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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DannyZ
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Re: Factory Dual Solex PDSIT Carburetor Adjustments

Post by DannyZ » Fri Mar 15, 2019 10:27 pm

Hopefully this can help clear up the vacuum hose limbo:
Yes, I know the correct vacuum source nipple for the preheater thermostatic valve and it is hooked up.
On my Central Idling circuit my vacuum nipple for where the mixture reference hose is supposed to connect is blocked off and welded shut (as is the big pipe right next to it that used to go to the air pump). Please see my pic and markings on your diagram to help illustrate this. Image
Image

So I am guessing that I am out of luck in this regard for using the central idling circuit to perform my mixture reference test? Any other ideas for:

Q#1: synchronizing my carburetor mixtures (step#4) since I am not able to perform the Mixture reference hose "ON/OFF" test with my set up (I do have an EMPI synchronizer gauge that has made a huge difference)?

Q#2: how to get the central idle mixture screw set just right since my set up doesn't allow for "finger ON/Off" the mixture reference hose as detailed in step#5b.

It makes good sense in your write up. It didn't miss my attention, I just didn't clarify my specific set up clearly enough. Again, sorry for that.
And I will block off the nipple off the right carb that was part of the EGR stuff. Should I also plug the other end of the mixture reference hose that goes into the bottom of the right booster elbow?
Attachments
InkedDualCarbDiagram2 -with my set up_LI.jpg
Central-Idling-circuit-plug.jpg
1974 Westfalia

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Re: Factory Dual Solex PDSIT Carburetor Adjustments

Post by Amskeptic » Sat Mar 16, 2019 5:02 pm

DannyZ wrote:
Fri Mar 15, 2019 10:27 pm

So I am guessing that I am out of luck in this regard for using the central idling circuit to perform my mixture reference test? Any other ideas for:

Q#1: synchronizing my carburetor mixtures (step#4) since I am not able to perform the Mixture reference hose "ON/OFF" test with my set up (I do have an EMPI synchronizer gauge that has made a huge difference)?

Q#2: how to get the central idle mixture screw set just right since my set up doesn't allow for "finger ON/Off" the mixture reference hose as detailed in step#5b.

If you decide not to hook up the thermostatic preheater valve to a vacuum source, you lose engineering that is friggen critical for good driveability.
I saw the photograph of your central idling plumbing, and I think you can just saw/dremel off that stupid weld job on the vacuum nipple so you can have a correctly functioning valve and preheater, AND do the mixture test.
Saw off the tip of the nipple. You only need 3/8" nipple remaining to clamp on the vacuum hose with. You can even drill out the thing if weld is still visible inside at the 3/8" mark. If you need to drill, you will need to remove the entire central idling plumbing, and I know you will too, because you care about a proper job and do not want drilling swarf in the intake passages! I just know it.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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DannyZ
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Re: Factory Dual Solex PDSIT Carburetor Adjustments

Post by DannyZ » Sun Mar 17, 2019 11:18 am

Awesome. All this makes sense. I will let you know how it all goes. Thanks again for everything here and your patience!
1974 Westfalia

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Re: Factory Dual Solex PDSIT Carburetor Adjustments

Post by Amskeptic » Fri Mar 22, 2019 10:04 am

DannyZ wrote:
Sun Mar 17, 2019 11:18 am
Awesome. All this makes sense. I will let you know how it all goes. Thanks again for everything here and your patience!
I'll wait here .. . . . .
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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DannyZ
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Re: Factory Dual Solex PDSIT Carburetor Adjustments

Post by DannyZ » Mon Apr 08, 2019 12:27 am

Just wanted to give a quick update. I was able to remove the weld and re-install the mixture reference hose where it needs to go. Makes every step now possible.
Everything is making more and more sense each time I work on these carbs. Thanks so much for everything.

Just for clarification, are the air horns still off for steps 4 and 5: Synchronize carburetor mixtures and Set Central Idling Speed/Mixture?

Thanks again for your patience and explanations!

[image][/image]
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IMG_9811.JPG
1974 Westfalia

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xyzzy
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Re: Factory Dual Solex PDSIT Carburetor Adjustments

Post by xyzzy » Mon Apr 15, 2019 4:06 pm

Also aren't your hoses on the right air-horn reversed? On my 73 (and in Colin's diagram), looking at the fully assembled air-cleaner and the right air-horn, the mixture reference hose should be on the *left* and the thermostatic valve hose on the *right*....

Image

Those are reversed....no?
---
1973 Westfalia
Encinitas, California USA

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DannyZ
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Re: Factory Dual Solex PDSIT Carburetor Adjustments

Post by DannyZ » Wed Apr 17, 2019 3:30 pm

Yes, these hoses were reversed. Now that I reconnected the mixture reference hose in the proper place, I have switched these hoses as well.
1974 Westfalia

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Re: Factory Dual Solex PDSIT Carburetor Adjustments

Post by Amskeptic » Wed Apr 17, 2019 7:45 pm

DannyZ wrote:
Wed Apr 17, 2019 3:30 pm
Yes, these hoses were reversed. Now that I reconnected the mixture reference hose in the proper place, I have switched these hoses as well.

Adjust mixtures with the air horns on!
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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DannyZ
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Re: Factory Dual Solex PDSIT Carburetor Adjustments

Post by DannyZ » Wed Apr 17, 2019 7:55 pm

Perfect! Thank you for clarifying that Colin. I figured but just wanted to double check.
1974 Westfalia

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Re: Factory Dual Solex PDSIT Carburetor Adjustments

Post by ktk833 » Thu Dec 16, 2021 11:13 am

Hi.
I need help... I'm really struggling getting a decent drive on my 2l Type 4 with the Solex PDSIT pair so far (recently fit in replacement of a pair of Zenith carbs for the 2.25l Land Rover).
1). Kindly tell me the best thing to do if my distributor has no retard vacuum- I've tried understanding what was stated in a reply above but can't make sense if it.
2). How do the thermostatic valves on the carb work? On the left carb ( cylinders 3/4, which seems to be my issue in my drive as the plugs are ALWAYS suited) the valve is open (blows threw) and no effect on temperature changes. The right carbs valve is closed and neither has any change on temperature. The cylinders on this side (1/2) seem to burn well as I have brown plugs and seem to be what gets me home after a long drag.
The van has evident smoke on driving and really drags...and on one or two occasions when it accelerated pretty well, the engine temperatures were so high, the vents were just smoking out.
Kindly help. I've tried following the step-by-step procedure in tuning up...

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satchmo
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Re: Factory Dual Solex PDSIT Carburetor Adjustments

Post by satchmo » Thu Dec 16, 2021 4:18 pm

If you don't have a working vacuum retard distributor, then Colin's tuning write-up will be no help to you. You will have to set your idle timing around 5-8 degrees BTDC and 28-32 BTDC at 3200 rpm. Idle speed will be faster than you like, but you will have to live with it until you get the right distributor/vacuum canister. Resist the urge to adjust the throttle plate stop screws to slow the idle speed.

There is only one thermostatic valve and it is located on the right air horn (the 'pizza slices' that bring air from the filter box to the top of the carbs). Maybe you mean the chokes. Each carb has one and you can follow Colin's instructions for checking to see if they work and for adjusting them. If you have a choke that isn't operating correctly, it will cause some strange running on that side of the engine.

Good luck, Satchmo
By three methods we may learn wisdom:
First, by reflection, which is noblest;
second, by immitation, which is easiest;
and third, by experience, which is bitterest. -Confucius

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Re: Factory Dual Solex PDSIT Carburetor Adjustments

Post by ktk833 » Sat Dec 18, 2021 5:30 am

Thanks Satchmo for your clear response and especially in regards to the retard vacuum.
On what I refer to as thermostatic valve (I got that name off the vw service manual), I am referring to some brass bolt component that is next to the overflow screw, next to the carb spray diaphragm. It is supposed to, on heating up at about 21 degrees, open to reduce the amounts squarted by the spray jet.
On one carb, the jet thing is open (I should believe already in fail-mode). On the other, the thing is shut but doesn't open on temperature change.
Well- thanks for the assistance this far.

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Re: Factory Dual Solex PDSIT Carburetor Adjustments

Post by ktk833 » Sat Dec 18, 2021 6:24 am

Hey,
Another thing, my carburetors only have the vacuum advance slots- no others for the retard... how then would I incorporate the retard to the right distributor???

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satchmo
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Re: Factory Dual Solex PDSIT Carburetor Adjustments

Post by satchmo » Sat Dec 18, 2021 7:12 am

Image

Image

Let's see if these photos help you clarify which thermo-switch you are referencing.

The first photo above shows a right hand side PDSIT carb. The throttle plate has a flat face that may or may not have had a thermo-electric valve attached. Most plates with this feature were blind castings, meaning there were no open ports and they were never meant to function with the thermo-electric valve. Most PDSIT carb throttle plates don't have this feature, and I think if your carb does, it can be safely set up with that face on the throttle plate blocked off.

The second photo shows the right and left hand PDSIT carbs. The left hand carb (it is the one on the right in the photo) is bigger because it contains the plumbing for the central idle system. Note that it also has a thermo-electric valve attached next to the idle air cut-off plunger (the thermo-electric valve is the rectangular box you see attached with two screws and it has an electrical spade connector on it). This valve was present only on the left hand carb, not on the right. In my experience, it is rare to find one that functions correctly. You can easily open it up and fiddle with it. Sometimes a new o-ring can get it working properly.

So which thermo-electric valve are you talking about?

For vacuum retard, only the left carb with the central idle system has a port for the hose connection to the retard side of the vacuum can of the distributor. This port is located on the throttle plate and it draws its vacuum signal from just below the plate, the area where the vacuum signal is the strongest when the plate is fully closed at idle.

Satchmo
By three methods we may learn wisdom:
First, by reflection, which is noblest;
second, by immitation, which is easiest;
and third, by experience, which is bitterest. -Confucius

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