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Mon Aug 31, 2015 4:24 pm

Hi all,
Trying to understand the theory behind the carb sync on the stock 32 PDSIT-2/3 carbs on my '65 Squareback. I searched a lot through past threads today and did a good bit of reading but I didn't really find anything that addresses my questions.

I'm using the German STE snail sync tool.

I'm finding that I can get the idle sync done no problem. The issue arises when attempting to sync above idle. The STE snail tool is calibrated in kg/h of air flow. At idle both sides are flowing about 7 kg/h.

Just above idle, the right carb swings up to 10 kg/h while the left carb barely budges off 7. I can get the left carb up to 10 if I really rev it up but of course by that time the right carb is up nearing 25-30.

Now supposedly if there is variation between the two carbs you are supposed to adjust the linkage rod to the right carb in order to bring them in line. However I don't really understand what adjusting the linkage rod is supposed to do and I would like to understand it better before attempting adjustment.

There's not really any real room for adjustment before a longer or shorter linkage rod would just be holding one of the throttle plates open and I don't think that's the intent.

It seems like the variation between my two carbs is so high that I can't see how adjusting the linkage would overcome it.

It just seems like the left side is not moving as much air as the right side. The carb-to-manifold bolts are tight, the vacuum hose for the advance (left carb only) is new and tight, the advance diaphragm in the distributor holds vacuum.

I got into doing this to try to understand the carb sync process better but now it looks like I need to go back to the beginning and verify mechanical condition first. So I guess my questions are:

1) What's the normal range of variability between the two sides and how much can you reasonably expect to compensate by adjusting the right side linkage rod?

2) Would unscrewing the the idle screw on the right side (i.e. closing the throttle plate) and screwing in the idle screw on the left side (i.e. opening throttle plate) to correct the idle speed make the readings more balanced above idle since the throttle plates would be starting from different positions when the linkage pulls them open?

My assumption is that adjusting the linkage is meant to take any slack out of the linkage so that both throttles begin being opened at the same time and at the same rate. Is that assumption correct? If so, it doesn't seem to me that adjusting the linkage would be sufficient to compensate for the variation that I'm seeing between the two carbs but I don't have experience with these carbs to know for sure. What do those who have experience say?

3) Should I, before doing any of the above, go back and check valve adjustment, compression, dwell and timing? I think I know the answer to this one :D

Thanks so much to anyone who can teach me something on this.

Mon Aug 31, 2015 4:37 pm

I am going to try and address a couple of things here.

1) I have never seen anyone mention sync beyond idle. You sync them at idle and let the rest fall as it may. Your initial sync is with all throttle arms off. Get the idle adjusted to your liking and then use your sync tool and the idle adjustment screw to get both sides in sync.

2) Once they are in sync you attach all of your throttle linkages and adjust them till you get back to sync with the linkages connected and not touching the idle screws. All of this adjusting should be with the linkages only.

Do you have a balance tube between the two carbs? If so, this should rule out most of the variability from side to side. Again, I have never seen anyone try and sync above idle.

Mon Aug 31, 2015 4:44 pm

Here is a video that helped me in my carb setup for 32's. All my experience before was with Kadron 40's and Dell 36's. I was completely new to 32 PDSITs.

https://www.youtube.com/watch?v=najLc9GlLJ0

His is a type 4 engine with a different linkage, but the theory is the same. He going into excruciating detail on some parts, but there is a lot to learn in that video.

Mon Aug 31, 2015 5:18 pm

one4house wrote:
1) I have never seen anyone mention sync beyond idle. You sync them at idle and let the rest fall as it may. Your initial sync is with all throttle arms off. Get the idle adjusted to your liking and then use your sync tool and the idle adjustment screw to get both sides in sync.

Ah but both the blue Bentley and the Look, Listen, Do It Better service bulletin describe that it is "essential" to check the sync at higher engine speeds. They say you should check it at 1200-1500 rpm and if the sync tool setting varies at this speed then you should adjust the right side linkage rod to bring them to the same reading. Then re-check at idle.

I will check out the video, thanks!

Mon Aug 31, 2015 5:23 pm

sjbartnik wrote:
Ah but both the blue Bentley and the Look, Listen, Do It Better service bulletin describe that it is "essential" to check the sync at higher engine speeds. They say you should check it at 1200-1500 rpm and if the sync tool setting varies at this speed then you should adjust the right side linkage rod to bring them to the same reading. Then re-check at idle.

I will check out the video, thanks!

I guess today was my day to learn something new. I had no idea.

I guess I will wait till someone who knows more than me chimes in. It shouldn't take long. :)

Mon Aug 31, 2015 6:01 pm

sjbartnik wrote: Hi all,

I got into doing this to try to understand the carb sync process better but now it looks like I need to go back to the beginning and verify mechanical condition first. So I guess my questions are:

1) What's the normal range of variability between the two sides and how much can you reasonably expect to compensate by adjusting the right side linkage rod?

2) Would unscrewing the the idle screw on the right side (i.e. closing the throttle plate) and screwing in the idle screw on the left side (i.e. opening throttle plate) to correct the idle speed make the readings more balanced above idle since the throttle plates would be starting from different positions when the linkage pulls them open?

My assumption is that adjusting the linkage is meant to take any slack out of the linkage so that both throttles begin being opened at the same time and at the same rate. Is that assumption correct? If so, it doesn't seem to me that adjusting the linkage would be sufficient to compensate for the variation that I'm seeing between the two carbs but I don't have experience with these carbs to know for sure. What do those who have experience say?

3) Should I, before doing any of the above, go back and check valve adjustment, compression, dwell and timing? I think I know the answer to this one :D

Thanks so much to anyone who can teach me something on this.

I would start by opening them up and determine what jets you have

-mains - what size (s) are they the same or different?
-Airs- ?
-Pilot jet size (are they electric)?
-venturi size- do they match
-Are your short throttle links the same?
-What is the length of your left side carb rod ? You can find the correct length center of cup to center of cup on here somewhere or buy the ISP set-up which comes with 3 fixed rods which eliminates that problem.

Use the manual "stop look listen ......" to get them set-up initially

You mentioned setting idle to 750 rpm in another thread perhaps..I have never been able to get my car to idle that low ( i use a 64 only distributor) mine is more like 850

Of-course setting them at 3k rpm helps and is actually more important than idle balance IMHO!

no adjusting the idle screws won't help at this point, they only help when idling. How can this carb stop help you when you are on the throttle?When the throttle cable is pulling the linkage away from the idle screw which is basically a stop there is no adjustment to help you balance- thus adjusting the right side carb link.

There is a special tool which attaches to the center pivot and helps me to set my rpm at about 3k so I can then adjust the 1/3 side carb rod (my others are fixed ISP west set-up)

sorry about the rambling answer

Are you planning to go to any shows coming up (Ct show 8/12 or Flanders 8/20)? I can bring the tools and we can work on it together

Mon Aug 31, 2015 6:04 pm

I've synced many dual carbs over the years - from DCNF to IDF to ICT to Kadron and dual Solex carbs on type 3s. After getting the carbs synced at idle with the linkage off I reconnect the linkage then carefully observe the movement of the throttle arms while slightly moving the linkage (always at the point where the throttle cable connects up - you don't want to distort the movement of the linkage) - adjusting each linkage until both arms come off the screw stops at the same time. Done! If you want to piddle around with trying to sync up a pair of carbs with a running motor thats fine - I like my method and it has worked for me for many years now. I'm sure there are other methods that work just as good.

Mon Aug 31, 2015 6:35 pm

sjbartnik wrote: one4house wrote:
1) I have never seen anyone mention sync beyond idle. You sync them at idle and let the rest fall as it may. Your initial sync is with all throttle arms off. Get the idle adjusted to your liking and then use your sync tool and the idle adjustment screw to get both sides in sync.

Look, Listen, Do It Better service bulletin describe that it is "essential" to check the sync at higher engine speeds.

I just reread that thing and found the part you mention. Funny to think that I printed off that "look, listen and do" as a guide when setting my carbs up a few weeks ago. Shows you how closely I read things when I'm doing something I am familiar with.

Much like OLD VW NUT, I have always done my sync with the arms off and then back on to make sure the throttles open exactly the same. Never have looked at the sync above idle. I guess it is all how you are taught. I assume either way works for all dual carbs once you figure out the intricacies of the adjustment.

Mon Aug 31, 2015 7:18 pm

EasternNotch wrote: [
-mains - what size (s) are they the same or different?
-Airs- ?
-Pilot jet size (are they electric)?
-venturi size- do they match

I found Keith's carb setup notes. So it would appear I have a 137 main jet on the right side and 137.5 on the left. Idle jet g50 (if I'm reading his handwriting correctly). I don't have any notes on the airs.

These carbs do not have the electromagnetic idle cutoff valves.[/quote]

Quote:
-Are your short throttle links the same?
-What is the length of your left side carb rod ? You can find the correct length center of cup to center of cup on here somewhere or buy the ISP set-up which comes with 3 fixed rods which eliminates that problem.

I will have to measure those but they seem to have the paint marks on them. The Look/Listen pamphlet also has the spec for length of the left rod and two short rods.

Quote:
Use the manual "stop look listen ......" to get them set-up initially

You mentioned setting idle to 750 rpm in another thread perhaps..I have never been able to get my car to idle that low ( i use a 64 only distributor) mine is more like 850

No I mentioned that the Look/Listen pamphlet says to set idle at 750 rpm but that contradicts blue Bentley which is basically 850 ± 50 which is where I like it to be. I set it closer to 900 rpm to be at the high end of the spec. It idles smoother up there and I like the idea of more cooling air over the engine, more heater output, and higher generator output at 900 rpm.

Quote:
Of-course setting them at 3k rpm helps and is actually more important than idle balance IMHO!

That is my thought too! I would rather have them balanced/synced at 3000 rpm than at idle.

Quote:
no adjusting the idle screws won't help at this point, they only help when idling. How can this carb stop help you when you are on the throttle?When the throttle cable is pulling the linkage away from the idle screw which is basically a stop there is no adjustment to help you balance- thus adjusting the right side carb link.

The way I'm thinking about it is like this, the idle screws are really throttle stop screws. When you screw them in you are opening the throttle plate more. So what I'm saying is if you were to adjust the idle screw so that the throttle is more open on say the left side than it is on the right at idle, then when you step on the gas the linkage pulls the throttles open but because they are starting at different positions, one throttle will be open more than the other one throughout the travel of the linkage. Right?

Still it seems to me you're not meant to do it that way in any case.

Quote:
There is a special tool which attaches to the center pivot and helps me to set my rpm at about 3k so I can then adjust the 1/3 side carb rod (my others are fixed ISP west set-up)

Yes I've been looking for that tool but have not found one so far yet.

Quote:
Are you planning to go to any shows coming up (Ct show 8/12 or Flanders 8/20)? I can bring the tools and we can work on it together

Definitely can't make CT show but possibly Flanders.

Mon Aug 31, 2015 9:38 pm

1. Are your valves adjusted and is your compression even? If not- adjust valves.
2. Make sure there are no vac leaks at the balance tube or at the carb/ manifold bases. Run your RPM up to 1500 and have an assistant spray WD-40 at the balance tube, manifold base, and carb body. Does that change anything?

3. If 1 and 2 are in order, most likely the low side has a "lazy link" somewhere- wear in a ball socket, wear in the throttle shaft ( but #2 would show that up) or a floppy transfer plate (the plate that the two rods pop onto)

Adjusting the rod on the "lazy" side will cure this. Shouldn't take much. If you have a floppy transfer plate, tighten it up!

A maladjusted "short" rod on the lazy carb (if yours are the adjustable type" can be a culprit here as well. Compare the length of the two short rods- they should be exact.

It's all about synchronicity, baby- try not to think about it or over analyze it too much- just do what they tell you!

Mon Aug 31, 2015 11:58 pm

Getting the carburettors synchronised just above idle will make the biggest difference to smooth power delivery during normal driving. (Assuming the other basics are sorted - mixture, timing and you're not running a 009 with built-in flat spot)

It took me a while to crack this on my squareback, the best write-up I found on the process was in the Muir manual - the Haynes doesn't mention it, and the Bentley (at least my copy) only mentioned FI systems.

Here is the process I followed:
• Sync the carbs at idle using the throttle stop screws
• Hold the throttle slightly open at around 1200-1500rpm
• Sync the carbs by adjusting one of the linkage rods

Just to make things a bit more tricky, sometimes wear in the bellcrank centre linkage means that depending how you hold the throttle open you may be biasing the linkage towards one side of the engine or the other. If so, when you remove the holding device and the throttle is opened bu the cable, the balance will be out again. Best way to avoid this is to hold the linkage by pulling on the cable attachment in the general direction that the cable pulls normally.

I had a friend who had access to machine tools knock up a nice contraption to make this job super easy, something along these lines is ideal, doesn't have to be this flash.

Tue Sep 01, 2015 6:37 am

Tram wrote: 1. Are your valves adjusted and is your compression even? If not- adjust valves.

This I will have to check. I am confident in Keith's ability to adjust valves and I've probably only driven ~1000 miles since I bought it from him but I do need to check for myself and get some baseline compression numbers noted as well so I can track trends in the future.

Quote:
2. Make sure there are no vac leaks at the balance tube or at the carb/ manifold bases. Run your RPM up to 1500 and have an assistant spray WD-40 at the balance tube, manifold base, and carb body. Does that change anything?

I was thinking this too. Will try.

Quote:
3. If 1 and 2 are in order, most likely the low side has a "lazy link" somewhere- wear in a ball socket, wear in the throttle shaft ( but #2 would show that up) or a floppy transfer plate (the plate that the two rods pop onto)

Adjusting the rod on the "lazy" side will cure this. Shouldn't take much. If you have a floppy transfer plate, tighten it up!

I will compare the length of both relay rods (the short ones) to make sure they match. I do see a wee amount of floppiness in the relay lever (what you are calling transfer plate) on the left side where as the linkage starts to take up it initially twists on its shaft before rotating whereas I don't see that same movement on the right side. How do I tighten up the relay lever/transfer plate?

If I were adjusting the rod on the lazy side (main linkage rod), I would shorten it, yes?

Quote:
A maladjusted "short" rod on the lazy carb (if yours are the adjustable type" can be a culprit here as well. Compare the length of the two short rods- they should be exact.

They are the adjustable type, I will check.

Quote:
It's all about synchronicity, baby- try not to think about it or over analyze it too much- just do what they tell you!

They told me not to adjust the left side linkage rod! :D

Tue Sep 01, 2015 6:42 am

Dodgy wrote: Getting the carburettors synchronised just above idle will make the biggest difference to smooth power delivery during normal driving. (Assuming the other basics are sorted - mixture, timing and you're not running a 009 with built-in flat spot)

Yes I can see how this would be so and currently with the left side being a bit lazy it can sometimes cause a bit of hesitation coming off idle, especially since the advance signal is coming from left side only.

I do not have an 009, I have the correct vacuum advance only distributor for this engine. The VW p/n is 311 905 205 D. I don't have the Bosch number handy.

Quote: Best way to avoid this is to hold the linkage by pulling on the cable attachment in the general direction that the cable pulls normally.

This makes sense, I'll keep that in mind.

Quote:
I had a friend who had access to machine tools knock up a nice contraption to make this job super easy, something along these lines is ideal, doesn't have to be this flash.

Nice! I noticed that the plans for local manufacture of the VW tool are available on this site; I wonder if I could take them to my local friendly metal fabrication shop and they could make one for me...

Tue Sep 01, 2015 8:31 am

Here is the original one or one variation of it. Mine is stamped VW 691/1

I have 1.5 of these just need to have the adjuster piece made that grabs the 3 arm pivot for the one on the right. I have been meaning to look into finding a way to fix this missing part :roll:

Edit:

the tool is stamped US 691/1

and I am willing to give measurements if anyone wants to have one made

Tue Sep 08, 2015 7:23 pm

EasternNotch wrote:

I have 1.5 of these just need to have the adjuster piece made that grabs the 3 arm pivot for the one on the right. I have been meaning to look into finding a way to fix this missing part :roll:

There is an ad here on the Samba for what I think you're looking for, see:

http://www.thesamba.com/vw/classifieds/detail.php?id=1551235

It's listed pending but that might just be because I asked him about it. The second photo which you can't see right now shows it's the bit with the knurled thumbscrew on one end and the socket for the 3-arm lever on the other. Might want to drop him a line.

Tue Sep 08, 2015 7:29 pm

OK I think I got this figured out.

Checked valve adjustment and they were a bit tight all around. Corrected that. Checked for vacuum leaks, none noted.

Put the Snail back on and still the same results.

Did as Tram said and shortened the left side linkage rod a couple turns and BAM it was right on the money, both sides opening equally and equal measurements on the Snail on both sides at idle and at ~1500 rpm.

Shortening the left rod had the effect of increasing the reading on the left side while simultaneously decreasing the reading on the right side. I guess that's the balance tube in action?

At any rate got it dialed in nice and it's much smoother in that transition from idle. Feels like it has more guts now too.

On careful inspection of the linkage, it appears that the relay lever bushing on the left side (the lever that the linkage rod attaches to and the spring attaches to) has some play/slop in it, likely due to wear. So while the right side relay lever pulls true and straight, the left side one torques slightly before it begins to open the throttle. It seems that it was this slop that was causing my problem. Shortening the left rod takes the slop out so that both throttles open at the same rate/same time. What a world of difference!

Thanks to all for the carb sync advice!

Thu Sep 10, 2015 7:43 am

Quote:

There is an ad here on the Samba for what I think you're looking for, see:

http://www.thesamba.com/vw/classifieds/detail.php?id=1551235

It's listed pending but that might just be because I asked him about it. The second photo which you can't see right now shows it's the bit with the knurled thumbscrew on one end and the socket for the 3-arm lever on the other. Might want to drop him a line.

Yeah I grabbed that off him, now I have both styles- anyway I am still planning to go to Flanders next weekend so maybe i'll see you there

Thu Sep 10, 2015 9:21 am

I'm going to try to make it.