34 PDSIT SOLEX CB Performance

[Frank Bassman]

BIG THANKS TO FREEBUG FOR ALL HIS HELP AND INSIGHT, he himself having these carbs and all.

Well I installed these carbs from CB performance recently and have been driving them around, getting used to them, and wanted to share my experience with them for whom it may concern!

Yea yea I could have put better carbs on my motor but I wanted these ones for their simplicity... and the Solex name... yea I'm missing a coupla' chromosomes!

The motor:
1700 cc type 1
CB Cheater cam
light flywheel
Dual Port rebuilt 040 heads, stock valves.
8.5:1 compression

So I bought the kit while CB had a promotion, don't remember how much % off but long story short it came out to roughly 400 bucks shipped, that price included 2 extra main jet pairs (145, 150), 2 extra idle jet pairs (55,60), 2x 28mm vents, and a sync tool. Maybe something else, cannot remember.

The kit itself was 300 bucks with air cleaners, manifolds, balance hose, fuel hose, linkage, hardware etc.

So first things first, the linkages is a pice of junk, but it is workable and I got it to behave well, consistently. But be prepared to deal with that. Not hard to do, but not everyone will want or know how to do it. Had some slop on the center pice, lateral, so it has to be taken out somehow. I was cheap and stuck a lot of aluminum foil in there. did the trick for now, eventually I will get a scat centerpull linkage so I'm not worried about it.

Next up, they come with puny 22mm vents from Brazil, so unless you drive anything smaller than 1500cc they may not work. Or they might if you get creative with jetting but it won't be optimal... so do as I did and get 28 mm vents, jet accordingly. In my case I started with 145 mains and left it there. They come with size 130 mains from the factory.

Next, idle jets were 50, but I went up to 55 from the get go. Even with 55's I get some lean behavior, I may bump it up to 60 idles and re adjust my mix. Doesn't stink like it's running rich and the plugs look very nice and clean so perhaps that's what sea level in Miami during summer calls for.

These carbs use a two jet air corrector circuit which I know next to nothing about except only one is removable. It looks almost like a main jet, but is not dimensionally the same. I left the 130 that was on there. Have yet to play with it but I don't think I'll have to.

Next up, the manifolds. Because I am a knucklehead, I have not taken pictures, but they looked very decent for the price of the kit. They seem to be aluminum aloy of some sort, I think I put a magnet on em when I got the kit to see but I don't remember. 90% sure they're cast aluminum. They look fine on the inside, mating surfaces were flat, no complaints there. They come pre-tapped for one hex plug on the front side and one nipple for a balance tube on the back, or front, however you wish to set the tube. Behind the shroud is where I put mine.

The kit comes with cheap looking black heat insulators for under the carbs... HEADS UP, the studs that CB provides will NOT let you install the insulators, they are too short. So I bought longer studs and installed, an $8 dollar venture, no big deal unless you need to do an on the run install and drive home... in which case the insulators can be omitted and installed later... like I did.

About the carbs themselves: To me, they looked nice. I will go ahead and say something that will get me crap, but whatever. I once bought a newer empty 34 pict and the casting was excellent, I would say better than these PDSIT's. Having said that, the casting is not bad, but just like any other new carb they have to be taken apart and cleaned, blown with compressed air. It is the nature of the manufacturing process to leave debris so don't skip this step, nothing is ever perfect and Murphy's law applies!

The accelerator pumps need to be adjusted, I did so with them installed in the car. Tight fit, but doable. make sure both spritz the same when you hit the gas and call it good, a healthy spritz, not enough to drown the motor, but just enough that it is a healthy squirt into the manifold.

Next up, the throttle plates. They looked fine to me, actually there is one brass plug on one of the plate assemblies that cracked the area around it ever so slightly but after looking from the other side and seeing that there plug was sealing the orifice well I decided it was fine, and it was.

Since these carbs are for smaller displacements, there is no hole on the throttle plates for idle. Bigger engines will require a small hole on the throttle plate. I drilled mine 1.54 mm, 0.060". (was a 1/16 drill bit from Harbor Freight) Engine idles at around 850 rpm with room to adjust idle up or down from there, so I figured the hole was the right size.

I chose to run the balance tube. So I synchronized them at idle and put the linkage on.

WAIT.

I had to shorten the passenger side linkage. I don't know if this was a freak occurrence, but I had to take off about an inch... or less. It was a trial and error thing with a grinder. Worked out fine and was easy but again, not for everyone.

When synchronizing these carbs with the crap linkage, make sure they open at the same rate... if they do not, find which is opening less, (assuming they both are at their throttle stops at idle) and play with bending the linkage up or down to take up the slack and achieve an even opening rate.

For some reason the ball end linkage stubs on the carb and on the linkage center piece are different sizes... so there will be some play by the carbs. So long as they rest on their stops and the carbs open evenly after the bending adjustment, this won't really matter. You can change the stubs on the carbs, CB supplies the right size with the kit, but I left the ones on there because eventually this linkage is going bye bye.

Aside from these shortcomings, I like them. They drive nicely and I am getting a consistent 25 mpg in the city, with traffic. I have not yet taken them on a long highway trip because the opportunity has not presented itself. But I would not hesitate to do so.

Ideally you'd want to use an SVDA on these. May have to jet them way rich with a centrifugal only. They like vacuum I have noticed.

Here is a whole slew of pictures for all to see.

Hope this commentary helps anyone eyeing these carbs. They didn't make my car a rocket, nor were they intended to. I just wanted new carbs, that are simple and will give little problems. They are just that, they really don't get simpler than this. Car turns on, 20 seconds and it is idling well, I do use the chokes and they work fantastic. I wanted to get away from manifold preheat also since my header doesn't provide enough warmth to make the 34 pict behave well enough down here.

I am overall satisfied. I do want to modify them to get the vacuum advance to come in sooner... not sure if I'll do so by re-soldering the throttle plates and making a smaller hole, and readjusting so the plate position at idle is closer to the drilling, or if I will extend the drilling down a bit on the driver side carb. Still giving it thought. One of them options is reversible though.




Here is a whole slew of pictures for all to see.

-Frank

[Kizbo]

Yep. Just about everything you describe above has been the same experience that I've encountered. My set came on a motor that I'd purchased from someone else, so I had to do the whole venturi & jet upgrade as well. I too, feel for the most part pleased with these carbs... they really aren't too bad once all the factory flaws are ironed out and corrected. And yes, that center-pull mechanism has some slop in it... so much so that is was causing the right carb to open earlier than the left. I was able to correct this with a little manipulation of the linkage, but I like your idea with the foil and may keep that in my bag of tricks.

One thing I wish that these carbs had different are the floats. With dual carbs that have to be identically precise, I personally would prefer to have floats with bendable tabs... unfortunately these are a once-piece plastic and float levels must be altered by the addition or subtraction of shims/washers. Mine had the slightest drip from the discharge tube that was due to float levels....and they were really really close.

Thanks for sharing your experiences.

[nshaddox]

so what is the reasoning behind increasing venturi size? increased A/F ratio? what venturi size does a stock 34PICT have for comparison? has anyone tried a set of these on a 1600dp?

[PumaVW79]

Great review!

But I disagree with this hole on the throttle valve, the system was not designed that way, it will not contribute on better performance, easier adjustment or better mileage at low/medium rpm. There's a separate circuit to this function.

To enrich the mix it's preferable to decrease the air jet or increase the idle jet -- which operate not only at idle, it's in fact a "lidle/low/medium rpm jet"

[FreeBug]

Nshaddox, variations of these carbs were used on the 1500 sp with 21.5 and 23 mm venturis, on the 1600 dp with 24 mm venturis, and on the 1700-2000 type 4 with 26 mm venturis.

Puma VW79, I don't think you understand the problem: without a hole in the throttle plate, when you adjust the throttle plates for a reasonable rpm (750-900 rpm), on a larger-than-stock engine, the throttle plate is so high it engages the progression circuits, making proper adjustments at idle impossible.

With a hole, the throttle plate can rest in the proper position at idle. That's it.

Frank, sorry not to have PM'd you sooner, will chime in soon. K.

[PumaVW79]

[FreeBug]

The stock 34 mm throttle bodies (type 4) have holes in them. That's where I got the idea....but they also have a separate idle system.

Drilling holes in the throttle bodies is standard procedure for tuning, look it up in the Solex manual. If the progression circuits are kicking in too late, you can file the throttle plate for it to let air through sooner, too.

Don't take my word for it...

http://oacdp.org/pdfs/solex.pdf

[Frank Bassman]

What Freebug said. Idle is too low without the hole, hence the need for it on larger engines. (Well, larger than smaller VW engines.) I went ahead and drilled them out because I knew it would be the case, he and I have similar motors. Mine is fractionally smaller though so maybe a slightly smaller hole would have been better. I have a tiny bit of hesitation which could be due to the position of the throttle plates, or lean idle jets. I will try the 60 idles, but if the hesitation is there still or it gets too rich I'll take the carbs off eventually and see how the throttle plates sit as of now. Then I'll try reducing the size of the hole from 1/16" (approx 1.58mm) to 1mm, or 1.25mm. I could just file the throttle plates and was thinking of that before seeing the manual. I though it would have been a hack way, but apparently it was suggested by solex. Cool! But that will be the last thing I try since these carbs are notorious for being touchy about throttle plate position and drilling and soldering holes is easy, filing the plate is fully destructive.

On a side note I used a vacuum gauge to see how much vacuum the driver and passenger side carbs show at the line to the distributor... both showed a little over 20 inches. I measured both carbs because I wanted to see if they were different, seeing that the passenger side has a larger diameter fitting and plug than the driver side.

With this test I was also able to see when the vacuum comes in, seemed like it came in reasonably quick to me. As I understand it SVDA cans need about 10 inches of vacuum for full vac advance? anyone know the actual number with certainty?


-Frank

[FreeBug]

There are a lot of different vacuum cans, even just for SVDA. They have a little number stamped on the arm.Most start around 8-12 "Hg.

Sorry, I don't have a Bentley manual at han right now.

[67rustavenger]

So I'm gonna do a little thread hi-jack here. After all the thread is regarding the PSDIT32/34 dual carb setup.
When setting idle after the carbs are synced. Do you do adjust one carb and let the other be a slave? Linkage attached. Or are they adjusted together while watching the syncro-snale making sure that the carbs are flowing at the same rate? Currently my idle is a little low (600-650rpm) and I'd like to get it up around 900+rpm.
Any input would be appreciated.
Thanks
_________________
I have learned over the years.
Cheap parts are gonna disappoint you.
Buy Once, Cry Once!

There's never enough time to do it right the first time. But there's always enough time to do it thrice.
GFY's Xevin and VW_Jimbo!

[Frank Bassman]

If you are using the stock linkage with the play in the ends, you won't be able to do the slave thing.

You'll have to sync at idle. Remember to pinch off the balance tube so you tube the carbs individually.

Get them right at idle and then make sure they suck equally as rpm increases.

I wedge my steering lock stick on the accelerator pedal at about 1500 rpm (no high precision needed here) and check vacuum readings with the snail. when they are equal you're done. You may have to bend the lagging side linkage a bit to get it right. Trial and error.

As far as mix screw I screw in until that side begins to miss. Then out until it runs best. Then from whatever that point is I add about 1/3 of a turn out.


If you have a good linkage you should be able to do the slave thing, though I personally prefer having two points of contact vs one.

-Frank

[67rustavenger]

No I use the same linkage that you are dealing with.
I'm currently running an oh oh 9 dist ATM. I Have a 010 dist on order from tasb that he is working on. Hopefully he can get it finished this week But in the mean time I'm just dealing with what I have on hand.
Thanks for the speedy response.
_________________
I have learned over the years.
Cheap parts are gonna disappoint you.
Buy Once, Cry Once!

There's never enough time to do it right the first time. But there's always enough time to do it thrice.
GFY's Xevin and VW_Jimbo!

[Frank Bassman]

Ok, so a bit of an update on these carbs.

Working great, still with a slight stumble in the mid-range.

So I started reading much deeper into the depths of the PDSIT's, specifically type 2 PDSIT's. (late bus.)

I was at a swap this weekend and picked up a very decent set of bus PDSIT's for 30 bucks... With the idea of making some observations on them without taking my carbs out. They are essentially the same construction.

Also I wanted to have extra throttle bodies to stash for doomsday, since they bolt right on. Vents also swap over and the jets too.

I believe these were for '74 auto bus. They have 26 mm vents, 137.5 mains, 50 pressed in jet and 175 air correction.

For all of those who are messing with these carbs, the "pressed in jet" is the EMULSION TUBE.

Yes, maybe some knew, but it took me forever and a half to find concrete evidence, in this thread....

http://www.thesamba.com/vw/forum/viewtopic.php?t=3...mp;start=0

The emulsion tube is intersected by the air correction jet to its right. THIS jet is changeable.

What I found is that the addition of air correction plus emulsion values hovers at around 220.

Ex.) CB comes with 130 air and 100 emulsion. (230)
Ex.) OG German auto Solexes I bought come with 175 air and 100 emulsion. (225)

I would bet money that if there was a way to pop out the 100 emulsion and replace it with a smaller one the stumble could be tuned out.

----------------------------OR-----------------------------------------

Changing the air correction for a smaller one probably achieves something similar. The question is

WHY did Solex choose this "dual air" jet configuration over the single one that is seen in regular pict carbs?

What are the nuances of changing emulsion jet size vs the interconnected air jet?

My guess is it has to do with less intuitive fluid dynamics, translating into different inlet fuel air "curves" and tip in/out, so to speak.

Has anyone experimented with pulling the pressed in emulsion jet out and swapping? If so, how does that compare with simply messing with the air jet?

My theory is changing the emulsion jet could have a greater impact on mid throttle transition than changing the air... The air having more of an effect at high rpm high vacuum scenarios.

Any experience?

I know, very few even bother with these carbs, but I like a challenge.

-Frank

[Alstrup]

To get rid of the stumble up both the main jet and the air jet. With 28-29 mm venturi it is not unusual to be in the 180-185 range on the air jet, and dependant on the engine and power outpout in the 150 - 160 range on the main jet.
For starters you can also just up the main jet 0,5 and see where that gets you. Sometimes it is enough. Sometimes an SVDA distributor is the solution. Many vaiables.

T

[Chad M]

Edit, re-read and I've got it figured now.

[Frank Bassman]

Yes, I happen to have a set of 150's which I will try next. Easiest to do, I think I will be able to install without removing the carbs.

Alstrup I am using an svda right now, Bosch 034. You know about these carbs, have you ever tried a vacuum only on these? (205T, M, K, or one of the old big cap ones)
Did they work well with this? I wonder if vacuum only is more suited than svda?

Also, which of these two combos do you think seems best for driveability and economy on my motor? (1699, 8.5:1 cr, cb cheater)

A) 26mm vents, 137.5 mains, 55 idle, 100 emulsion, 130 air

B) 28mm vents, 150 main, 55 idle, 100 emulsion, 130 air

I can also substitute air for 175 on either combo.

Current combo is like B but with 145 mains.

Thanks for chiming in by the way, always great to get advice from you.

-Frank

[Slow 1200]

I would not use vacuum only distributor unless the carb is setup for that (vacuum drillings in the venturi)

[dawie]

On these carbs, emulsion tubes are fed different to most carbs.
Discharge nozzle is fed by inner of emulsion tube, instead of the more common way of connecting to the cavity around the emulsion tube.

The extra air jet in the "upper cavity plug" is just an air bleed hole to prevent syphoning under certain conditions. Thus situated in the uppermost part of channel feeding the discharge outlet. Needed because, in this arrangement, the air corrector no longer fulfills this function. Not connected to the air correction jet's channel.

Air correction jet and main jet feeds cavity around emulsion tube. Bottom of emulsion tube is closed.

Something like this:

or:

[Frank Bassman]

That diagram is exactly what I needed. I see now. Seems like the two possible solutions are raise the main jet or decrease the air jet. Or both. I will up the mains to 150 and see where that gets me.

It makes sense that if the main can't keep up with supplying the idles and the main in that high transition spot there will be a lean spot. Of course with stockish sized vents this is less touchy but with oversized ones of course things get a little more picky.

Thanks for the intel!

I'll change the mains and report my experience. I think I'll be able to do this without removing the carbs. Wish me luck.



-Frank

[PumaVW79]