PIERBURG Rebuild - pre build advice

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h11poc
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Re: PIERBURG Rebuild - pre build advice

Post by h11poc » Sun Jun 06, 2021 8:26 pm

The original tube is long gone !! I may have to improvise.,.. But the positive is that even if I cant get this pierburg to work for me it has new gaskets and a new wax stat and has been cleaned so will benefit someone else. I am awaiting arrival of the coolant hoses and then I shall be starting the car up and from there I can work out where I need to go. I wouldnt know about the little reducer but im thinking the speaker wire i cut , the end would fit in there and has a smaller hole thus reducing flow.. Possibly enough to mimic the original.. Today i made the clip between the auto choke and the lever with coat hanger making sure I got the right length and it appears to work as it should.



h11poc
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Re: PIERBURG Rebuild - pre build advice

Post by h11poc » Mon Jun 07, 2021 6:39 pm

Also , I worked out what the other port on the front was for. It ran to a "depression switch for gear change" which I don;t have on mine so I simply blocked it off. The schematic in Section c really does help.

Im not sure how this will all work out but I will be starting the car tomorrow since the rebuild so fingers crossed it will be ok.



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Re: PIERBURG Rebuild - pre build advice

Post by mark1gls » Mon Jun 07, 2021 11:05 pm

Let us know how it all goes..


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GT_II
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Re: PIERBURG Rebuild - pre build advice

Post by GT_II » Tue Jun 08, 2021 12:18 am

A minor issue worth checking is the auto choke earthing ring, which bridges the plastic choke mounting frame providing electrical continuity for the auto choke's heater element. The auto choke would still open without it, as the coolant flowing through the auto choke warms up, but not as quickly as it should with the electric heater element working.

The earthing ring is unbelievably flimsy and was broken on mine:

Pierburg 2E2 choke earth ring.jpg

Rather than fabricate a new ring, I made up a short earth wire to do the job:

Pierburg 2E2 choke earth wire.jpg
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h11poc
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Re: PIERBURG Rebuild - pre build advice

Post by h11poc » Tue Jun 08, 2021 2:47 pm

Hi all, so first run of the car and this is what happened. I saw the 3/4 unit open as it should , the autochoke did work as i saw the flap open when it got hot. I was running this wihtout the airbox on. However, the car keeps running when I turn it off although not running as in revs , more like a "pop pop pop pop and the carb vibrates and then it dies. I tried the timing and distributor but they are fine.
Also, it would not rev below 1200 revs so maybe the other screws may need adjusting ??

Anyway , what on earth would make the car run on after the ignition is switched off?? It didnt run on previously



GT_II
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Re: PIERBURG Rebuild - pre build advice

Post by GT_II » Tue Jun 08, 2021 6:13 pm

There's an electric fuel cut off solenoid around the back which cuts the fuel off when revs are above 1200 rpm and throttle closed to save fuel, which also helps to increase engine braking when you're slowing down. It's also needed to cut the fuel and stop running on when the ignition is switched off. Maybe yours has failed and someone has modified something to provide a fix?


1992 VW Scirocco GT II 1.8 90PS Brilliant Black 30k
2011 VW Caddy Van C20 Startline 1.6 TDI 102PS 60k
2015 Skoda Yeti SE Outdoor 1.2 TSI DSG 105PS 30k
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WreckTangle
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Re: PIERBURG Rebuild - pre build advice

Post by WreckTangle » Tue Jun 08, 2021 6:24 pm

When you turn off the ignition does the 3/4 point unit fully withdraw its plunger and then extend it again as the vacuum subsides? Have you attached the electrical connections correctly? There should be a wire to the idle overrun control valve. When you switch off the engine you will have vacuum on the lower port of the 3/4 point unit and the upper port will be "blocked" by the closed overrun valve. Under these circumstances the plunger should fully retract.

As for the high idle, can you see what is keeping it high? Is it the wax stat or the 3/4 point unit? Or possibly even a badly adjusted throttle cable? Have you set-up the high idle to 3,000RPM (with a hot engine and the lower vacuum hose removed from the 3/4 point unit) by turning the screw on the right-angled bracket in towards the plunger to increase and away from it to decrease idle speed? Having set that and reattached the lower vacuum hose can you adjust normal idle to an acceptable level using the hex nut on the back of the 3/4 point unit?



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Re: PIERBURG Rebuild - pre build advice

Post by WreckTangle » Tue Jun 08, 2021 6:52 pm

Also, does your wax stat mechanism have the adjustment screw present and tightened? In this pic of one of mine (with the throttle mechanism removed) you can see the screw I mean between the two plates on the wax stat mechanism. If present it’s obscured by part of the throttle assembly in your picture. People who mess with these carbs often lose that screw when they’re fiddling.
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h11poc
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Re: PIERBURG Rebuild - pre build advice

Post by h11poc » Tue Jun 08, 2021 8:16 pm

Ty gtii and wrecktangle

To answer the questions I do have the screw between the wax stat plates. The one thing I can say is that I don’t see the plunger withdraw when engine is off. The 3/4 is the right measurement extended and does retract , however I can not adjust idle because even when the wax stat comes on the throttle plate doesn’t close enough to make contact with the 3/4plunger.
It is almost like the throttle doesnt close. Using an Allen key I can manually turn the wax state plate but th throttle will not close to reduce idle.
Is there anything else apart from distributor, 3/4 unit or wax stat which would keep the revs high and also keep the engine popping when ignition off. It’s almost like it’s still getting spark.
It’s really odd as all units seem to be working .
I could take a video tomorrow if it would help?



GT_II
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Re: PIERBURG Rebuild - pre build advice

Post by GT_II » Tue Jun 08, 2021 8:51 pm

It's a few years since I checked the settlings on mine, but I remember one of the adjustment screws on the wax stat mechanism had been incorrectly tampered with to compensate for the lack of functioning wax stat. I found this because, after fitting the new wax stat, I found the idle with the engine warming up was too low, but I guess the opposite is also possible.

This seems to be a 2-step process - check the warm up curve (Pargraph 2.1 of Section B of the Pierburg manual), then set the throttle plate gap for the warm up mechanism (Paragraph 2.2). I wonder if one of these setting on yours has been tampered with. I have a feeling that one of these settings may be non-adjustable on later carbs, leaving just the the other one to check, but my memory may be playing tricks here.

The supplement to the Pierburg manual gives a very detailed explanation of the operation of the 3-point unit and associated components under the heading "Functions of the Throttle Plate Actuator" - well worth a read.


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WreckTangle
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Re: PIERBURG Rebuild - pre build advice

Post by WreckTangle » Wed Jun 09, 2021 12:38 am

Are you definitely getting a good flow of coolant through the auto choke and the wax stat? While you had the carb apart did you run water through the auto choke? They have a tendency to block. Across the three units I cannibalised to build my working carb one was totally blocked with radweld and another was blocked right up inside with part of an inlet manifold o-ring. If you’ve now got everything assembled on the car your best way to check is whether the hoses get very hot very quickly. If they don’t you’ll have to investigate.

Setting up the warm up curve is a black art for which you will need that tool I referred to in a previous post. You have to check the position of the throttle control on the physical curve in accordance with figures 24 and 25 in the manual. These correspond to the wax stat at cold and normal coolant temperature.

So, to summarise, you need to see if your wax stat is getting enough flow of coolant to extend properly and if it is what position on the curve it is getting the throttle to - should look like figure 25. At this point the 3/4 point unit should be able to control the throttle.

You do have the abutment screw in the angled bracket and it is lined up with the plunger on the 3/4 point unit? Some people adjust the throttle plate actuator by bending that bracket the abutment screw is set in. If this has been done to an extreme to compensate for other problems you might not have enough adjustment left in the abutment screw. But don’t mess with this until you’re confident the wax stat is working properly and the throttle is on the right point of the warm up curve at normal operating temperature.



h11poc
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Re: PIERBURG Rebuild - pre build advice

Post by h11poc » Wed Jun 09, 2021 12:05 pm

Ok, so I have spent a couple hours so far. This is what I have seen and noticed.

The two plugs going to the unit above the 3/4 unit have 12v when engine switched on and 0 when off.
The Wax Stat is working as I saw it move the spring and lever. All coolant is hot and flowing nicely.
There is a really strong smell like the fuel is way too rich , it smells like exhaust fumes.
The Autochoke is fine.
The It idled at 1500 rpm with the wax stat working and throttle closed. The screw wasnt even touching the 3/4 point unit .
The only way i can get the idle down is to move the distributor but every single time it runs on.

I may need to do a video ?? Its running on like a flap is open keeping petrol flooding into the engine for twenty seconds after car is turned off.

Depression plunger on 3/4 unit I can only see working on startup and so on. Maybe if I record it on camera and it doesnt move all the way back in when i switch off this would be the problem??



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Re: PIERBURG Rebuild - pre build advice

Post by h11poc » Wed Jun 09, 2021 1:44 pm

So I got a neighbour to turn the car off. The idle is not about 1100 which is better than it was and I can adjust that with the screw if nned be I guess. But when the neighbour turned the ignition off the plunger on the 3/4 unit didnt retract any further than it does when its at idle. Then two seconds later it returns to the start up position which is keeping the throttle open and the car splutters ...



WreckTangle
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Re: PIERBURG Rebuild - pre build advice

Post by WreckTangle » Wed Jun 09, 2021 5:14 pm

The crucial thing is whether, when the wax stat is at normal operating temperature, the throttle mechanism is at the correct position in the warm-up curve per figure 25. If it is, then you can adjust the right angled bracket and abutment screw to make contact with the 3/4 point unit. You do this first by setting the notional high idle to 3,000RPM as previously described.

Does the 3/4 point unit fully retract if you block the top port and draw a vacuum on the lower port? If so, there is probably something wrong with your vacuum tubing or the over-run switch.

Those wires should go to 12V when the ignition is switched on. I think at least one of them is switched via one of the temperature senders, but I don't know very much about them. They seemed to work OK on my car, so I left them alone.



h11poc
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Re: PIERBURG Rebuild - pre build advice

Post by h11poc » Wed Jun 09, 2021 5:41 pm

Sorry Wrecktangle , explain the thing about the top port block. Do I take the hose off the 3 point unit or where it connects to?? And how do i draw a vacuum on the lower port?? By sucking the hose ??

All the vacuum tubing and T pieces are brand new. All correctly attached as per the diagrams thanks to GTii and yourself.