Tips from Drew21
the channel heater unit should get a permanent 12v and is earthed through the carb, if not working check the volts at the connector and check the carb earth strap
3/4 point unit, when you turn the engine off the piston should fully withdraw and the extend to its starting position. Failiure to do this indiates a fault with the overrun solenoid.
pull down unit
to check for vac leaks in this unit attach a pipe to the lower port and unplug the upper port. Suck on the pipe. The arm should move a small amount and then stop when the vac collapes. Then if you put your finger over the upper port ad keep sucking the arm should withdraw a bit more and hold vacuum. If it fails to hold vac then replace.
hot air flap, this can seize during the summer as it doesn't get much use. So as the weather gets colder its worth spraying ome WD40 on this and making sure it moves
poor running can be caused by air leaks around the base flange, can be a cheap fix if you're having problems with missing at idle. To locate vac leaks try spraying gamping gaz (carefully) around the vac pipes and the base of the carb. Changes in idling should be heard when you find the leak!! Tips from Mark25
some stuff about the part throttle channel heater:
With the ignition off and the heater supply wire dissconnected, the resistance of the heater is about 3.8 ohms measured back to the negative of the battery. So this value includes all the wiring and earth straps back through the carb and engine.
With the ignition on and the heater supply wire connected, I have 11.3 at the heater supply wire. Therefore I am loosing about 0.5v across the switch or relay that controls the heater.
I think the symptoms if it?s not working are; the car runs rough until the engine is totally warm. You can get round this with a manual choke by just leaving it out longer. With mine I can put the choke in as soon as I?m out the drive way, in all but the coldest, ie -5oC, weather.
EDIT: the above tests were done on a unit that had been transfered to a weber.Tips from EZ_Pete on pulldown unit replacement
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 above, 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.
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 below for a table of the settings for all the various engine codes
Please reply if you've done this by an easier method.
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
Audi 80 1.6CL / '83-'86 / DT / automatic
Audi 80 GL & Coupe 1.8 / '83-'86 / DS/NE / manual
Audi 80 GL & Coupe 1.8 / '83-'86 / DS/NE / automatic
Audi 100 & Avant 1.8/ '83-'87/ DS / -
Golf/Jetta/Scirocco 1.6 / '83-'92 / EW/EZ / manual
Golf/Jetta 1.6 / '83-'92 / EW/EZ / automatic
Scirocco 1.6 / '83-'92 / EW / automatic
Caddy 1.6 / '83-'92 / EW / -
Golf/Jetta 1.6 Cat. / '86-'92 / RF / manual
Golf/Jetta 1.6 Cat. / '86-'92 / RF / automatic
Golf Cabrio/Scirocco 1.8 / '83-'92 / EXZ / manual
Golf/Jetta/Synchro 1.8 / '84-'92 / GU / manual
Golf/Jetta/Synchro 1.8 / '84-'92 / GU / automatic
Scirocco 1.8 / '86-'92 / EXZ / automatic
Golf/Jetta 1.8 Cat. / '86-'92 / RH / manual
Golf/Jetta 1.8 Cat. / '86-'92 / RH / automatic
Passat 1.6 / '83-'88 / DT / manual
Passat 1.6 / '83-'88 / DT / automatic
Passat 1.8 / '83-'88 / DS / manual
Passat 1.8 / '83-'88 / DS / automatic
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