How to change your 2e2's pulldown unit

I shall abbreviate pulldown unit to PDU for convenience .

I'm going to assume that you have tested the old unit in accordance with Drew21's method detailed in post 2 of the rubjonny FAQ, and it has failed. You should also check carefully all the vac hoses going to the PDU and replace if they look anything but recent. The one that goes down to the bottom of the carb from the "A" port on the PDU may degrade/perish due to proximity to manifold warmth.

Tools required:

In order to show the process clearly, I've photographed a stripped-down carb, and you'll notice that the PDU is incomplete too...but not in any relevant sense.
I managed to change one of these without stripping any parts from the carb, but it is a bit tricky, as the autochoke assy is rather in the way.

Judicious juggling and bending can remove the old (easy 'cos it doesn't matter if it breaks) and insert the new; you run the risk of snapping plastic parts, however. You may prefer to make a note of approx. how far the adjustment screw protrudes into the 'slot' and then remove it to make insertion easier. Access to replace this screw isn't that nice however, as it's from the rear of the carb, and there are parts in the way, as always. I think it is the safer option probably.

Of course removing the autochoke assembly makes the job easy, but you may not need to if you are brave (the bendy method), or nimble-fingered (screw out method).

View of PDU in-situ. The red arrow shows the direction it moves when the diaphragm is 'pulled' by vacuum. The green arrow points at the part that actually touches the choke flap linkage. The blue arrow shows the stop that limits its overall movement:


The pin securing it:

Knocking it out/down:

The adjustment screw:

Access to adj screw:



Once you've got the new PDU in and secured with the pin (I think you even get a little 'grippy washer' that fits over the stop too), you will want to set it up for your carb. Don't attach the vac hoses yet, you can set it up without even starting the engine. You just need one longer hose attached to the lower port "A", that you can suck on.

There are two adjustments, the black circular part at the front adjusts the first stage , the little Allen screw mentioned above sets the second stage. Look up the settings required for your engine code, my manual transmission EZ requires 2.8mm and 5.6mm for the two stages. Find some drill bits or similar of the right diameter, measurement is down the front edge of the choke flap, between it and the edge of the barrel.

With a completely cold engine, so that the choke spring holds the flap shut, suck on port "A" with port "B" open to atmosphere. You should see the flap open about the right amount, adjustable by screwing in, or out, the round plastic bit. Once you're happy with that, you can set the second stage by continuing to suck on "A" but now with "B" blocked with a little finger. You will find that the choke flap opens more now. If this second stage needs adjustment it's that little Allen screw round the back. You may struggle to do this while sucking and blocking things, so cheat! Just manually pull the long plastic part of the PDU forwards, as far as it will go. If that's too far you need to screw the Allen screw further in, and vice-versa.

Now you can plumb it all in with the correct vac hoses, and away you go.

See post #3 below for a table of the settings for all the various engine codes

Please reply if you've done this by an easier method.

 

think this needs adding to the FAQs section.

Well done pete. Yet another interesting read

 

Am doing this job tomorrow along with the waxstat hope its as straight forward as it looks thanks for the help pete-gd man!!

 

Car / years / engine code(s) / transmission
Pulldown gap, first stage (a), mm
Pulldown gap, second stage (a1), mm

Audi 80 1.6CL / '83-'86 / DT / manual
2.6
5.0
Audi 80 1.6CL / '83-'86 / DT / automatic
2.9
6.0
Audi 80 GL & Coupe 1.8 / '83-'86 / DS/NE / manual
2.6
4.9
Audi 80 GL & Coupe 1.8 / '83-'86 / DS/NE / automatic
2.7
5.1
Audi 100 & Avant 1.8/ '83-'87/ DS / -
2.6
4.9
Golf/Jetta/Scirocco 1.6 / '83-'92 / EW/EZ / manual
2.8
5.6
Golf/Jetta 1.6 / '83-'92 / EW/EZ / automatic
2.9
6.0
Scirocco 1.6 / '83-'92 / EW / automatic
2.9
6.0
Caddy 1.6 / '83-'92 / EW / -
2.8
5.6
Golf/Jetta 1.6 Cat. / '86-'92 / RF / manual
2.5
5.0
Golf/Jetta 1.6 Cat. / '86-'92 / RF / automatic
2.9
4.8
Golf Cabrio/Scirocco 1.8 / '83-'92 / EXZ / manual
2.5
4.9
Golf/Jetta/Synchro 1.8 / '84-'92 / GU / manual
2.5
4.9
Golf/Jetta/Synchro 1.8 / '84-'92 / GU / automatic
2.3
4.7
Scirocco 1.8 / '86-'92 / EXZ / automatic
2.7
5.1
Golf/Jetta 1.8 Cat. / '86-'92 / RH / manual
2.1
4.4
Golf/Jetta 1.8 Cat. / '86-'92 / RH / automatic
2.1
4.4
Passat 1.6 / '83-'88 / DT / manual
2.6
5.0
Passat 1.6 / '83-'88 / DT / automatic
2.9
6.0
Passat 1.8 / '83-'88 / DS / manual
2.6
4.9
Passat 1.8 / '83-'88 / DS / automatic
2.7
5.1

In every case a rather tight tolerance is suggested of +/-0.2mm for the "a" dimension and +/-0.15mm for "a1" Can't really believe it's that critical myself .

 

Feel free .

I did hope to get some feedback from cmanr (if he's done the job now) or others who may have changed theirs. It's not a difficult job, but I was hoping between us all we could devise a 'minimum-grief' method. I've not tried the hypothetical "remove the adjustment screw" method, so I don't know how hard/fiddly it would be to re-fit. I'm pretty sure access round the back there is impeded by the secondary vacuum unit, but maybe with the screw blu-tacked to the end of an Allen key it's quite OK?

Judging by the number of secondhand carbs I've got with broken PDUs it's a very common failure, along with waxstats of course .

 

Over-complicating things is a bad habit of mine...
That was pretty much my approach, but I was a bit worried about breaking my new PDU.

 

Sorry i didnt get back sooner been abit busy!!well the waxstat was straight forwards but for the pdu i found that if you screw the bolt in just enough then it will fit through the hole and sit in place,then all you need to do is adjust it using the appropriate allen key-this is quite tricky!!oh and i didnt cheat(only because i forgot! )but now runs alot better so thanks for the help Pete!!