Non return valve-pierburg 2e2

Hi to all! I am Goran from Bosnia. I have Jetta MK2 with pierburg 2e2 carb. I found this on internet and I would like to hear yours opinions:

"The Mistake in the Haynes manual and on the bonnet diagram.

On the inlet manifold, there is a vacuum supply to the advance retard mechanism, brakes, the choke pulldown unit and the (carb) three point unit. Part of the system consists of a vacuum store (a green globe) and two non return valves, which look like inline fuel filters, and are half black, half yellow. One of these is usually fitted the
wrong way round, because of a series of mistakes by VAG and Haynes.

Follow the vacuum pipe from the green vacuum store, to a t piece that goes into the carb, and then to a non return
valve. The YELLOW end should point towards the vacuum store, not (as shown in Haynes and on the underbonnet diagram)
the black side.

A symptom of this is the choke pulldown unit not working, the idle being very low when the car is cold, poor
performance when the engine is cold, constant stalling when cold, etc etc.... ".

Source: http://www.pistonheads.com/gassing/topic.asp?h=0&t=759057&d=10886.20095&nmt=

Thanks

 

This is wrong. VW didn't make a mistake.

The pulldown unit works just fine with the valve in the orientation that VW put it.

The non-return valve, and that connection between the pulldown unit and the brake servo vacuum hose is not well described by Haynes, not at all.

I'll try to explain what I mean during my lunch-hour.

 

"This is wrong. VW didn't make a mistake.

The pulldown unit works just fine with the valve in the orientation that VW put it.

The non-return valve, and that connection between the pulldown unit and the brake servo vacuum hose is not well described by Haynes, not at all."


Ok i see that both of us are online right now but ill wait for your lunch brake .
So what is wrong? In Haynes, chapter Fuel and exhaust systems - carburettor models 4A21, fig. 19.4., non-return valve orientation is: white(yelow) side to brake servo and black to pull down unit! So direction is from brake servo to pull down unit!
And you just said "connection between the pulldown unit and the brake servo vacuum hose is not well described by Haynes, not at all"
In the other hand, u said "VW didn't make a mistake. The pulldown unit works just fine with the valve in the orientation that VW put it."

I am so glad that you answered to me becouse i read your posts for few years and you are "god for carburettors", as we said in my country. Cheers!!

 

Sorry Goran, I was in too much of a hurry earlier, that wasn't a clear answer I gave.

You are correct about the Haynes Golf II manual, it shows the valve the correct way round. Same as on the bonnet stickers, same as VW built. Air can only flow towards the green ball vacuum reservoir (and pulldown unit) through the valve. I'll explain why I think this is correct, later.

What I had remembered (wrongly) was a written description of how the pulldown unit works, which was partly misleading. Looking in the green-cover version of manual number 1081, it does show a vacuum pipe diagram for pierburg 2e2, Fig. 3.33, probably the same one you mention. But the written text I was thinking of is not there.

I think the text may be in this manual instead: http://www.amazon.co.uk/Pierburg-Ca...58/ref=sr_1_34?ie=UTF8&qid=1330430980&sr=8-34 I will check this evening.

I will refresh my memory later when I have all the information available, then I may be able to say something that is clearer.
I think this connection, valve and the green ball are more to do with ignition timing control, than pulldown unit function.

 

Right, so I have the red-cover Haynes 1081 now, and their "Solex & Pierburg Carburettors" manual, volume 1785 by Charles White.

The red 1081 has the same diagram as the green one, as I expected. It does also have some text about the Choke pull down unit, which I won't type out in full here, except to point out the mistake:-

[page 4A.18]

Err, isn't that maybe the 2e3 carb, on the 1.3 engines...
ThermoTime valve on the 2e2 is used to control the primary throttle position during the early stages of cold-start, not the pull-down unit.

So no help from 1081.

The Pierburg carbs manual, 1785, has a bit more detail:-

I can scan-in Figure 7.9 if necessary later.

Most of that makes sense to me, except for the part that I've highlighted in red. I think this part is what has inspired the 'wrong way round non-return valve' theory, because it could only be a good description if the valve was the other way around, allowing manifold vacuum at the brake servo junction to 'suck' air from the green ball and/or pulldown port B. With the valve orientated the way VW put it, air can only go the other way, towards green ball and pulldown port B.

Time for a little rest and a glass of wine.

 

So why do we have a vacuum reservoir and a tee'd connection from it to both the pulldown unit and intake manifold?

Well according to the text from manual 1785, it's about going from the first stage of pull-down operation to the second stage, at a suitable rate. Well I can see how a vacuum reservoir like the green ball could pause/slow down this process, by connecting into the pulldown unit as the valve inside it opens at the end of the first stage opening. There would be no more opening until the green ball/vac res was emptied of air. We know from here, that you only need to block port B of the pulldown, not suck on it, to get the pulldown to move to stage 2, gap 'a1', as long as port A is still getting sucked. So that could work; but why the connection to the brake servo line via a non-return valve?

I don't know. It doesn't seem necessary if this is all the green ball is for.

Alternative theory involving distributor vacuum advance coming up in the next instalment.

 

Now I don't know enough about ignition timing/mapping to support this properly, but consider what happens as the accelerator pedal is 'stomped on' from a low-revs, light throttle cruise operating point.

The primary throttle plate is forced open, fairly rapidly collapsing the vacuum in the intake manifold. Assuming that we are not being silly and driving like this on a cold engine, the pulldown unit will have finished its work some time back, with the bimetallic coil spring in the autochoke housing having fully opened the choke flap. So the pulldown unit cannot affect anything now.

The revs will be rising, but not very quickly at first unless a very low gear is selected or the load on the engine is very low (e.g. downhill).

So if nothing else was involved, the vacuum advance supplied by the diaphragm/linkage on the distributor could rapidly disappear. It will take a while for the centrifugal advance to build with increasing engine revs. So the timing advance would be at a minimum.

Is this undesireable? I'm not sure. Hopefully someone will tell us!

What I can imagine is that the green ball reservoir, and the link via the non-return valve right next to the point where the distributor vacuum feed comes from, might provide a time-buffer to allow the engine to build speed and replace vacuum advance by centrifugal advance, before the vacuum signal to the dizzy is lost by the filling of the manifold. Picture the rush-in of air being diverted to fill the green ball, before this change of pressure can affect the distributor.

The connection to the pulldown unit serves only to re-evacuate the green ball after such transitional conditions have passed.

Discuss.

 

I'll re-plumb my vac gauge to be between nrv and green ball, to look at some of those ideas.

 

But the only thing on the carb that is connected to the green ball is the pulldown unit, which isn't needed for more than half a minute from even the coldest of coldstarts.
Almost all of the vacuum-using functions of the carb are only active at idle and/or during coldstart anyway. The obvious exception is the secondary throttle vacuum motor, but that isn't connected to the pulldown unit at all, externally or internally AFAIK.

But the non-return valve as fitted at Wolfsburg is the wrong way round for this. As soon as you put your foot down flat, or switch off the engine, the green ball fills to the same pressure as the inlet manifold, pretty rapidly.

Agreed, but for those sort of things, it's clear why a steadyish source of vacuum is required. As I said ^^, the carb seems to need 'a lot' of vacuum, as judged by the number of vac hoses, but most of that isn't doing anything during fully-warmed-up part-throttle-or-greater driving.

Not according to my vac gauge, it's filled in 2 seconds, because the non-return valve lets air towards the green ball and pulldown unit any time the manifold is at a higher pressure than those bits.



Much as it might look otherwise, I really am keen for input from anyone and everyone on this. I'm really not sure about my ignition timing theory.
Any experts reading who know what should happen at 'tip-in' - transitional between vacuum advance conditions and mechanical advance operating area - to minimise hesitation???. Could do with another vac gauge to plumb in so I've got gauges at green ball t-piece and at the dizzy vac diaphragm, to see if there is actually a time lag of vac change at the dizzy, which goes away if you take the green ball out/block that pipe. Might be able to do something with video I guess, moving the gauge around between 'takes'.

What I did observe with the vac gauge 'reading' the green ball was that it takes longer than I would've expected to be evacuated from start-up, and after a WOT. I think that may be due to the length of the vac pipe to my gauge (2m?) and the tiny orifice in the t-piece that feeds it, and the tinyish orifice in the carb vac nipple that feeds port A of the pulldown. More experimenting needed to check that.

 

OK. I get it. Thanks to you two guys now i understand how pulldown unit works!
Again, thanks to you two and lots of yours posts,I found out that my pulldown unit, TTV and his fuse, and heater in choke cover are not good!
So, after i changed all that, made settings for 1st and 2nd stage of pulldown unit, checking all hoses and put new flange there is a new problem!
Its cold start problem!
But, at first, after i put these new parts, motor starts prety fine and i saw that pulldown unit reaches first stage (at first begining, choke plate was fully closed). I was so happy.
And, in the morning ! motor wont start.
I was rushing to work and i have to put some metal plate to open choke palte that i can start motor and drive!
After work i made a test. While motor runing I was pull out vacuum hose from lover port (A) and put finger on the hose. There was no vaccum activiti from carburettor at all!
Please help![:^(]

 

There must be a blockage in the vacuum nipple at the base of the front of the carb, I think.
I'll have a look through my photos, to see if I have one of this port, close-up. I seem to remember that the hole inside this nipple is very small, maybe 0.5mm, so could get blocked up quite easily.

Edit:
I can't find a photo of the pulldown unit vac source, but this one shows the nipple at the back of the carb which feeds the 3-point unit. You can see how tiny the hole in the middle is. I think the pulldown vac feed nipple that goes to pulldown port A looks similar. Try poking a very thin wire into it.

 

John, I think maybe it is all just to do with the pulldown (until someone who knows lots about ignition advance tells me my theory might be right!), and the connection to the manifold/servo hose is only to 'refill' the green ball after shutdown. But I'd be quite surprised if the seal of the valve inside the pulldown is good enough to need such a feature.

Of the three vac sources at the back of the carb, two are side by side below the butterflies, feeding 3PU and airbox thermostat, the third one is at about venturi height IIRC, feeding the secondary throttle vac diaphragm. The top feed usually shown as a red hose, is a supply of atmospheric pressure air from the very top of the carb.

 

That sounds like an almost perfect description, as I understand it, except I'd probably refer to the green ball emptying of air, rather than filling up with vacuum - same thing though.

 

Well, Pete, you were right! . That vacuum nipple at the base of the front of the carb was blocked! I hardly found so thin stell wire to pass in. I would check that erlier but I thought that this nipple hasnt so tiny passage becouse on the front there is at least 2 mm wide hole, bat inside there is barely 0,4 mm wide hole! Whatever, now choke is ok, but I have few more questions to finish my carb service.
1. How high idle (rpm) need to be on cold start?
How to setup that?
2. Now, I cant reduce my idle below 1200 rpm when motor is on fully warm temperature!
How can i resolve this? Maybe on screw that is in plate of throtle?
My 3-point unit seems to work just right it should! But screw on it doesnt work enough to reduce that idle!
3. What is the right way to setup corect warming curve?

I supose that all of those questions are related!
Thanks again Pete and John!
Sorry for my english!
Cheers!

 

Hi Goran, I'm glad we are making progress.

I'm working on an answer to your 1, 2, 3 above, but I want to make it as clear, picture-enhanced and complete as possible, so I can copy it into a future FAQ-type thread. Should be done by the end of the day.

Your written English is better than that of many people who were born here.

 

Hello Goran.
There are (at least) two possible reasons for the fully-warm idle being too high.

1. Someone has moved the 'screw that is in the plate of the throttle', causing the normal 13mm 'nut' adjustment on the rear of the 3-point unit to not have enough adjustment range.

2. The expansion element (waxstat) and its cam/mechanism - on the other side of the carb - is actually still governing the idle speed even with the engine fully warmed up. This may occur if the waxstat has lost some of its wax, or if it is not getting hot enough due to a problem with the coolant supply to it.

So how to tell which reason is the problem?

Have a look at this picture (taken when my engine was not fully warmed up), and compare it to what you see when your engine is fully warmed up, idling at the 1200rpm.
Is there a gap between the 3-point unit's piston and the fast-idle adjustment screw, as there is in this image? Try sliding a piece of paper between these things,as the gap may be small and hard to see. If there is a gap, then number 2 is a problem, the waxstat stuff is still governing the idle speed.



If there is no gap, then you need to check the position of the fast-idle screw in the throttle plate. There is only really one way of getting this right, and it seems strange. The first thing to realise is that 'fast idle' speed is a theoretical thing, never experienced during normal operation; but it is useful in setting up the carb if it has previously been 'played with'.
The second thing to note is that the fully extended position of the 3-point unit doesn't change with the 'normal' idle speed adjuster on the back of the unit, so is a good reference point from which to get everything else correct.

With fully warmed up engine remove the vacuum hose shown below from the 3-point unit. This sends the piston of the 3PU to maximum extension. This hose is not easily accessible, but if you 'push' it off with fingernails or similar from the extreme end of the rubber hose rather than trying to pull it off, you may find it easier. The revs should rise rapidly up to about 3000 rpm. Check your rev counter and make a note of what it says. Avoid the temptation to switch the engine off with the ignition key at this point, yes 3000rpm(+ maybe) sounds loud and may be disturbing your neighbours, but, with the throttle quite wide open, the engine will try hard to keep running even with ignition off, and this may cause very unstable combustion events. Instead, go back to the engine bay and push the vacuum hose back onto the 3-point unit.

I must emphasise that if you attempt this process with anything other than a fully warmed up engine, the results will be useless and may cause you new problems.

Now; if the revs went to more than 3000, you need to unscrew the 'fast-idle' screw away from the piston of the 3-point unit. Some oil on the thread near the plate, and a pair of pliers will be necessary to grab this 'headless' screw. If the revs were less than 3000, it will need to be screwed in towards the piston. Small adjustments and repeat testing are advised.



Only when this theoretical fast idle speed is approx correct does it make sense to try to adjust the 'normal' idle speed with the 13mm spanner, only with a fully warmed-up engine, and after any waxstat-related faults have already been fixed.

With regards to what is the 'correct' idle speed at first start-up and throughout warm-up, this is very temperature dependent. As long as the engine keeps running, and doesn't sound like it is 'revving its nuts off', it isn't critical.

Edit: If neither the waxstat seems to be giving trouble, nor the fast idle screw; one other possibility is that the vacuum nipple circled in black in post #13 is partly blocked. Horrible to access with the carb mounted, but worth checking.