PDSIT Idle

[Dave105]

Hi all, well this is my first post to this form, although I've been an avid reader for the past 6 months (since I got my first van).

My question is this; Ive just had my carbs refurbished, stock duel 34 PDSIT Solex, The problem is I cant get the central idle system to bring the revs below about 1200. Talking to the guy who refurbed them he seemed to think that it was the problem of the 009 dizzy (which was on when i bought the van). I beleive that this set up origionally ran a dual vac dizzy (cant see one for sale for love nor money) and the vac retard has somthing to do with the idle setup?
Anyone shed any light on this or know where I can get a dual vac dizzy?
Thanks in advance!!

[satchmo]

Hi all, well this is my first post to this form, although I've been an avid reader for the past 6 months (since I got my first van).

My question is this; Ive just had my carbs refurbished, stock duel 34 PDSIT Solex, The problem is I cant get the central idle system to bring the revs below about 1200. Talking to the guy who refurbed them he seemed to think that it was the problem of the 009 dizzy (which was on when i bought the van). I beleive that this set up origionally ran a dual vac dizzy (cant see one for sale for love nor money) and the vac retard has somthing to do with the idle setup?
Anyone shed any light on this or know where I can get a dual vac dizzy?
Thanks in advance!!

Your mechanic is correct. You need the dual vac (advance and retard) distributor to get the central idle to work correctly.

Spend a little time looking for a distributor in the classifieds here and on theSamba. Sometimes you can find a working dual vacuum can that you can install on a regular single vacuum dual advance (SVDA) distributor.

New SVDA distributors are available through AirCooled.Net and other vendors, while a new dual vacuum can is listed on the Bus Depot web site(http://www.busdepot.com/details.jsp?par ... 021905271E). It is a pretty expensive item there, but if money is no object...

Good luck and welcome aboard. Tim

[Dave105]

Thanks for the info Tim. One question, by your reply I assume that the workings/advance curve is the same for both single and duel advace dizzy, the only thing different is the vac-can (and that a dual vac-can fits on a single vac dizzy?)

I was also told that a single vac dizzy off a Type 1 engine fits a Type 4 do you know if its true?

Thanks again.
Dave

[satchmo]

Thanks for the info Tim. One question, by your reply I assume that the workings/advance curve is the same for both single and duel advace dizzy, the only thing different is the vac-can (and that a dual vac-can fits on a single vac dizzy?)

I was also told that a single vac dizzy off a Type 1 engine fits a Type 4 do you know if its true?

Thanks again.
Dave

The advance curves (mechanical and vacuum) are pretty close but not the same on all the SVDA and DVDA distributors. Check out all the specs on this site (http://www.oldvolkshome.com/ignition.htm). The vacuum cans are completely interchangable from an SVDA to a DVDA. And yes, a type 1 distributor from around the same year (late 60's through the 70's) will work in a type 4.

So you have a lot of options to put something together that will work with your carbs and get the central idle back (at least much better than the 009 will). Where you set the timing will depend on what distributor you have and how much advance and retard it produces, not on what the original engine specs were. I wanted to get my 1973 bus back to stock so I found a 205J distributor and bought a new dual vac. can back when they were relatively cheap. The stock PDSIT carbs with the central idle work sweet when you have all the correct parts.

Tim

PS: I just noticed you are from Manchester. I was a 'Scouser' for three months last Spring as I was attending a course at the School of Tropical Medicine in Liverpool. I sure had fun watching Man U and Chelsea duke it out for the championship.

PPS: You can modify any dual vac can to increase the retard it produces by doing a little filing on the actuator arm. Ask me how if you are interested.

[satchmo]

I found this for not too much. (http://www.thesamba.com/vw/classifieds/ ... ?id=411546) You may find something similar on your side of the pond with less shipping.

Tim

[Dave105]

Just to keep anyone interested updated on this.
After much scratching of the old noggin and a lot of rude words i discovered that the PO had blocked off the central idle system using a 1/2in bolt in the rubber pipe from the idle mech!!! Removing this allowed the idle air screw to start to do somthing! Still have the problem with the fast tickover but after a visit to Vanvest this weekend i ended up with 5 dual vac cans, getting em home I found one works so was pleased with that as they only cost £10 for the lot. Will try and get one good dist out of the lot (never striped one down before any one got any advice?)
Also got one comming from a guy in the US so between his and mine might be able to get somthing working!

One last question. should i time with the vacs connected?

Thanks and will keep you posted

Dave

[satchmo]

If the vacuum can is an unknown as far as the advance and retard it produces, you will need to time with hoses off (disconnect at the dist. and plug the hose with a golf tee or something). Timing should be set at about 28 degrees BTDC with engine running 3000 to 3500 rpm (this is called max mechanical advance). Idle timing will then have to fall wherever it falls. Make a note of what you end up with.

To get an idea of how much vacuum advance and retard your dist. will generate, you will need to get creative. Keep the hoses disconnected and plugged. Keep your timing light and tach hooked up. Put another hose on the vacuum can and apply vacuum (sucking on the hose is probably the easiest method). The advance side should add about 7-12 degrees of timing. The retard side should subtract anywhere from 11-18 degrees. Once you know how much retard your vac. can produces, you can use this as a reference for idle timing.

For some advice on distributor rebuilding, check this site: http://www.glenn-ring.com/010/

Tim

[Dave105]

Hi Folks

Just to let you know what’s been happening.

I managed to source a DVDA dizzy and fitted it the other day. The 009 that was in caused me a few problems. When setting up the engine to No1. TDC and removing the cap I found that the rotor arm was pointing at No1 plug but not lined up with the notch in the dizzy body. It was in fact 90 degrees out! Then I couldn’t get the darn thing out. Turned out the tinware had been put on after the dizzy and was trapping the clamp underneath, a few bashes with a knocking stick and she was free.

New dizzy went in no probs, new vac hoses to advance and retard, set the points and she started 1st time!!!!!!

Setting the timing with both hoses on(?) at 4 ATDC (red dot on timing scale) and revs dropped to about 800RPM.
Disconnected Idle solenoid and then removed cutoff solenoids in turn: LEFT carb went down to ~500RPM, RIGHT wouldn’t idle. Opened idle adjusting screw (as per Bentley) and got a huge backfire through right carb. Flames and everything!! Screwed it back in and seemed OK again.

Only thing is when I reconnected the idle solenoid there is now no idle "suck", as if solenoid is stuck on seat? Playing around more I managed to stall engine and now it wont start!!

A couple of questions which some of you might be able to answer:
1 Will the van start without the idle circuit?
2 should there be a big vac signal on the advance line at idle?
3 how much should disconnecting the retard line alter the timing and what kind of vac signal should be there at idle?

I will endeavour to start it over the weekend and will let you know how I get on.

Thanks for your patience in reading all this

One other quick question---On the 72 oil bath air cleaner does the vac take off for the heated air intake (the vac-can flap thingy) come from the left carb manifold, as mine is coming from the body of the cleaner? I guess the little temp sense gizmo shouldn’t leak vac? Can you still buy these?

O-so many questions so little time!!!!!

Thanks again

[satchmo]

Hi Dave -

I don't know why no one else is answering you. Perhaps you should send a private message to Amskeptic since he is the dual carb guru here.

Anyway, are you sure all your solenoids are working correctly (with ignition key on but engine not running, disconnect and reconnect wires from each solenoid one at at time. They should make a nice clicking sound)?

Let's go back and begin the process of setting up your carbs correctly. Since you have a '72, you might want to take a look at this web site: http://www.ratwell.com/technical/FAQ.html Scroll down the left hand side on that page until you get to item 2.14 'Dual Carbs'. From there, you can get step by step instructions (with pictures!) on how to tune your carbs, and where all the hoses go.

I would recommend you start again making sure your adjustment screws are all out 2.5 - 3 turns (this includes both volume mixture screws at the base of each carb and the idle speed and mixture screws). Try to start the engine again and let it warm up so the chokes are not an issue (take a look down the carbs and be sure). Don't worry about the timing now. Just rotate the distributor a little (leave the clamp slightly loose) until you find it runs decently. Now go through the process of balancing air flow through the carbs and setting up the throttle cross bar for equal opening of the right and left throttle plates (see Ratwell's write up for this).

After those steps are done, you can balance contribution of each carb by disconnecting the pilot cut-offs, measuring rpms, making slight adjustments to the volume mixture screws, and then put the idle circuit back in the picture by reconnecting the idle cut-off solenoid and retard hose (give the throttle a little bump to get the rpm's back up).

Now you can work on timing and idle speed adjustments. Good luck. Let us know if you have more questions.

Tim

PS: at idle, there is no vacuum in the vacuum advance hose, but there should be a large vacuum signal in the retard hose. Think about it. The advance hose comes from a port above the closed throttle plate at idle, so there isn't much vacuum there. The retard hose comes from a port just below that closed throttle plate where there is a huge vacuum from the cylinders trying to get air across the closed throttle plate. When the throttle opens, the vacuum below the throttle goes away, but now there is an increase in vacuum above the throttle at the carb venturi, which is what we need to draw fuel into the carb and create a vacuum signal in the advance hose. Hope that helps.

[Dave105]

Thanks for the info again Tim all useful stuff

I had a look at a spare right hand carb last night to see where the vac advance/retard comes from. As you say the retard port is just below the closed throttle plate and the advance from above/level with it. As I seem to be getting a large vac on the avance at idle and no vac at retard, does this mean my throttle plate gap may be incorrect?
Looking at the Ratwell link:

Throttle plate - needs to have the correct gap. You will need a set of metric round feeler gauges in the 0.5 - 1.5mm range. This step is very important because it syncs the throttle position before any further syncronization is done (you will have to resync from here because the engine breathing will probably vary from one cylinder back to the other). 1 1/2 turn out from closed is a good starting point if the carbs are already mounted to their manifolds. You need to perform this step with the cross bar disconnected so it doesn't influence the setting

Do I set the throttle plate gap (by adjusting the stop screws) then re-adjust the fast idle linkage? I seem to be missing my stop screws so I guess whats fixing the throttle plate position is the fast idle cam/linkage?

Another interesting find: my ballance pipe/servo hose looks like it was leaky. Its about 1/2" (12mm) diameter off the manifold and then the solid pipe is more like 3/8 (10mm). The PO had used a lenght of 1/2in pipe straight from the manifold to the balance pipe so i dont think the vac connection could be that good.

Anyways thanks again for your help, will keep you posted

Dave

[satchmo]

Thanks for the info again Tim all useful stuff

I had a look at a spare right hand carb last night to see where the vac advance/retard comes from. As you say the retard port is just below the closed throttle plate and the advance from above/level with it. As I seem to be getting a large vac on the avance at idle and no vac at retard, does this mean my throttle plate gap may be incorrect?
Looking at the Ratwell link:

Throttle plate - needs to have the correct gap. You will need a set of metric round feeler gauges in the 0.5 - 1.5mm range. This step is very important because it syncs the throttle position before any further syncronization is done (you will have to resync from here because the engine breathing will probably vary from one cylinder back to the other). 1 1/2 turn out from closed is a good starting point if the carbs are already mounted to their manifolds. You need to perform this step with the cross bar disconnected so it doesn't influence the setting

Do I set the throttle plate gap (by adjusting the stop screws) then re-adjust the fast idle linkage? I seem to be missing my stop screws so I guess whats fixing the throttle plate position is the fast idle cam/linkage?

Another interesting find: my ballance pipe/servo hose looks like it was leaky. Its about 1/2" (12mm) diameter off the manifold and then the solid pipe is more like 3/8 (10mm). The PO had used a lenght of 1/2in pipe straight from the manifold to the balance pipe so i dont think the vac connection could be that good.

Anyways thanks again for your help, will keep you posted

Dave

You are on the right track, Dave. I would get those throttle stop screws in to get the correct gap. Too much gap will cause the throttle plate to actually cover the orifice of the retard port and wipe out the retard signal to the distributor. Too little will make the throttle sticky. Once the choke is open, there isn't much control of the throttle plate via the fast idle links unless things are screwed down way too tight. I think it is important to get the initial gap correct even if it means taking your carbs off again (not that hard, really). This will allow you to check out the fast idle cams and links, and make adjustments there as necessary. Check this site out for some more good pics of the carbs, especially the fast idle cam. (http://www.benplace.com/west_carbu_rebuilt1.htm)

Any air leak downstream of the air cleaner intake is bad. That is called un-metered air and it will make adjustments difficult, if not impossible, plus may burn your valves (leaks at the brake booster elbows are probably responsible for a lot of valve failure in dual carb buses). Find and fix any leaks at the balance tube, brake booster elbows, etc. Check out Amskeptic's diagrams on this thread (http://www.thesamba.com/vw/forum/viewtopic.php?t=64533).

Good luck, Tim

[Amskeptic]

Throttle plate - needs to have the correct gap. You will need a set of metric round feeler gauges in the 0.5 - 1.5mm range. This step is very important because it syncs the throttle position before any further syncronization is done (you will have to resync from here because the engine breathing will probably vary from one cylinder back to the other). 1 1/2 turn out from closed is a good starting point if the carbs are already mounted to their manifolds. You need to perform this step with the cross bar disconnected so it doesn't influence the setting

Do I set the throttle plate gap (by adjusting the stop screws) then re-adjust the fast idle linkage? I seem to be missing my stop screws so I guess whats fixing the throttle plate position is the fast idle cam/linkage?

Ratwell's 1 1/2 turns is a tad extremely excessive. To set your throttle stop screws, just turn them out counterclockwise until you see daylight between the screw on the lever and the boss of the carb. Turn in until contact, add a half a turn, yer done (later, you can synchronize airflow at idle by minor tweaks here).
Vacuum retard signal comes from left carb throttle body. I read your response above that said "spare right carb" and was confused.

Another interesting find: my balance pipe/servo hose looks like it was leaky. Its about 1/2" (12mm) diameter off the manifold and then the solid pipe is more like 3/8 (10mm). The PO had used a lenght of 1/2in pipe straight from the manifold to the balance pipe so i dont think the vac connection could be that good.

Clamp it down.

Please note too that the central idling circuit cutoff (the big honker on the left carb) does not just magically reinstate the central idle when you plug it back in. You have to blip the throttle to kick it back in. Don't know why, but it sometimes just sits there after you plug it back in and a throttle blip wakes er up.

Another note, the fast idle links are out of the picture entirely when the chokes are open. When you set the chokes, they will push open the throttles. Because you also lose all vacuum retard AND kick in the centrifugal advance with barely open throttle plates, the fast idle links have a quick effect on cold engine fast idle. Don't be clumsy here or you will have racing idles the likes of which we have not seen since these buses were new and everyone was confused. I do the fast idle link adjustments on a warm engine by closing the choke plates manually and setting the fast idles to 2,800 rpm with perfectly equal airflow. This is not Bentley prescribed, but it woiks for me arright??
Colin

[Dave105]

Guys, Thanks for all the very useful info, slowly starting to understand how these carbs work and how to set em up.

I have a couple of Muppet moments to admit to:

1) I did indeed look at a left hand carb, the one with the "big honker" cutoff circuit. why I said right I will never know
2) Looking at the carbs again and sticking my head right into the engine bay the missing stop screws were in fact there, the bit I was looking at was the 'throttle stop tab' on the bracket.

As I said so much to learn..........

Anyways back to the van.

Re-read Benson, Ratwell and Amskeptic info. As I changed both carbs and fitted a new DVDA dizzy, I didn’t have any fixed point to start from so did a lot of twiddling until everything seemed to run as it should. Took it for a test run and it drove like a bear, no pull at all. To cut a long story short what appeared to be happening was this: I set the timing to 5degs ATDC (both hoses on) small vac signal on advance hose strong signal on retard. When revved to 3000rpm retard signal disappeared advance vac came on strong. But letting revs drop to idle again timing went to 16deg BTDC and stayed there. Pulling the advance pipe off the timing immediately dropped back to 5ATDC reconnecting the advance pipe timing stayed at 5degs

Is it possible that the advance vac is not 'bleeding' away and is staying in the line? (hooking a vac gauge up to the advance vac line there is a slight vac signal at idle)

I don’t think the vac can is sticking otherwise why would the timing drop back as soon as the advance line is pulled off?

One question about setting the throttle position, can I use strong retard and or weak advance signal (at idle) to gauge the correct throttle gap?

Once again thanks for all who are replying to this thread your help is much appreciated, and needed.

Dave

[Amskeptic]

Anyways back to the van.

Right old chap, we call these mini-lorries "buses" here Stateside. . .

Is it possible that the advance vac is not 'bleeding' away and is staying in the line? (hooking a vac gauge up to the advance vac line there is a slight vac signal at idle)
One question about setting the throttle position, can I use strong retard and or weak advance signal (at idle) to gauge the correct throttle gap?

Good perceptive feedback and analysis here, Dave. Indeed you have a kerblooey situation here. The vacuum advance must not offer a signal at idle. The nipple is on the left (American driver's side, Queen's passenger side) carb halfway up the body of the carb facing somewhat towards the left rear "wing?" corner of the car. It must not have a vacuum signal at idle. It generally begins to read airflow around 1,100 rpm, but this could possibly be occurring at lower rpm IF the synchronization between the carbs is grossly favoring the left carb. More likely in my experience, is the gasket between the throttle body and the "carburettor" body may be misaligned or incorrectly cut. It is a weird gasket with an ovalized slot that must be correctly oriented.
Cheerio,
Colin

[Jaffa]

Dave

I suggest you get a hold of Colins tuning procedure for these carbs (either on this list or the Samba). This is what I used to set up the carbs on my 74 1800 AW. Easy logical step by step processes that work. The engine now has much more power and runs sweetly.

One point though regarding the thottle plate gap, the Bentley gives a figure for this, which I used initially, and I could not get a slow enough idle. I then adjusted the throttle using Colins method and all was good and I could actually tune the carbs.

The question I do have on this Colin, is I have a Gregory's manual from Australia which mentions that you should have no throttle gap if the thottle plate has a relief drilling in it ( ie a small hole). The PDSIT's I have have this small hole in the throttle plate. This seems to fit with your process for setting throttle gap?. Have you come across this before??

Cheers,

Craig