Pierburg 2E3 choke

[bigherb]

Hello all

Well, the garage is half way there with our van’s choke problem! The lever that CJH kindly supplied fitted and works just fine (thanks again, CJH) – now it looks like the Bi-metal choke isn’t working correctly. The engine starts on choke without any problem, and happily sits on fast idle, right up until the moment that the throttle is touched – at which point, the choke shuts off completely, and the engine stalls. Gowers and Lee can’t supply the Bi-metal choke, as it’s no longer manufactured, so I’m looking for one second hand. Does anyone have one, or know a good source, please? Three pictures attached; Gowers and Lee say the Pierburg part number is 4.07262.54.0. Thanks again!

Ian.

I don't think that is the problem.
If the choke comes on and goes off then bimetal coil it is working and it wouldn't cause it to stall when it comes off. Have they connected the electrical cables up correctly.

[CJH]

Three pictures attached

Those pictures come out quite small when 'attached' - can you upload the originals to Photobucket and then post links to them? With the small images it's difficult to be sure, but the bi-metallic coil doesn't seem to be obviously damaged.

Fast idle works the same way on mine - i.e. you set it with the accelerator pedal before starting, and it comes off as soon as the throttle is touched once the engine is running. So the trick is not to touch the accelerator until the engine's had a little while to warm up. The choke flap should gradually open as the bi-metallic coil warms up, either from the integral heating element (can you see whether that's intact behind the bi-metallic coil?) or from the heat of the coolant.

[kevtherev]

Hello all

Well, the garage is half way there with our van’s choke problem! The lever that CJH kindly supplied fitted and works just fine (thanks again, CJH) – now it looks like the Bi-metal choke isn’t working correctly. The engine starts on choke without any problem, and happily sits on fast idle, right up until the moment that the throttle is touched – at which point, the choke shuts off completely, and the engine stalls. Gowers and Lee can’t supply the Bi-metal choke, as it’s no longer manufactured, so I’m looking for one second hand. Does anyone have one, or know a good source, please? Three pictures attached; Gowers and Lee say the Pierburg part number is 4.07262.54.0. Thanks again!

Ian.

I don't think that is the problem.
If the choke comes on and goes off then bimetal coil it is working and it wouldn't cause it to stall when it comes off. Have they connected the electrical cables up correctly.

I can agree with that.
The choke richens the mixture, it should take 8 mins to open fully from fully closed.
coming off the choke resumes the mixture back to normal, if normal is too lean then it will stall

[ian prior]

Thank you, folks. The garage has tested for power to the heating coil, and is sure it's working correctly; the bi-metal coil is intact, and the engine runs on choke just as you say it should. I'll maybe ask them to richen the mixture slightly, but, aside from that, I think it's now all systems go for another year of camping all over the country!!

[CJH]

I've bought a cheapo vacuum pump to make it easier to check and set the choke pull-down, and to check the secondary throttle operation (especially with my new lever part installed). It works a treat, but I've discovered that only one out of the six pull-down units that I've got will hold a vacuum. The one that does is the original one on the LT carb I bought recently, but neither the one on my 'normal' carb, nor the the one on my 'test' carb will hold a vacuum. That's odd, since they're not more than two years old. They open under a vacuum, but they will gradually close unless I keep pumping - which implies a small leak somewhere. On an engine, where the vacuum is constantly 'pumping', it's not a serious issue I think (yet), but a leak anywhere is a bad thing.

I've also bought a pack of extra thin pipe cleaners for cleaning out the fuel and air channels, and some small graduated syringes to check the volume of fuel being pumped by the accelerator pump. I AM going to get this 'test' carb working properly! (although maybe not until a new pull-down unit arrives).

[CJH]

I checked and adjusted the accelerator pump today. First I measured the amount of fuel being pumped. I turned the injector so that I could get my measuring syringe under it:


Then I primed it by pumping a bit into the syringe, which also took me onto the graduated section - 0.8ml


Then I pumped it 4 times - one second for a full turn of the throttle and three seconds between each pump. After 4 pumps the level went over the top of the scale. I guestimated it to be 5.2ml


So ( 5.2 - 0.8 )/4 = 1.1ml per stroke. The VW factory manual says it should be 1.35ml +/- 0.2ml, so it's a bit on the low side.

I adjusted the cam all the way to the left to increase the volume, but I also had to bend the pump arm a bit to take out the initial slack. So that's the maximum I can get it to pump. It went up to 1.175ml per stroke, so just above the minimum.


Finally I adjusted the injector so that the jet of fuel cleared the groove and the side of the venturi.


That's as good as I'm going to get with that adjustment I think, an I'm hoping it will have improved the hesitation. But I also found a split in the bung that I've put over the unused vacuum spigot round the back of the carb. That won't have been helping a smooth idle. Just need to check the float valve/level, and put a new pull-down unit on now.

[kevtherev]

I can do that, thanks CJ

[CJH]

There's very little in the way of adjustment though, so provided the basics are right (no air leaks, clear jets, rubber bits and vacuum bits in good order etc) they ought to just work.

Whoever wrote that clearly didn't know what he was talking about. There's plenty to adjust, and even more to check.

I checked the float level and valve. The VW factory manual doesn't seem to cover it, but that 2E3 maintenance document gives a method of checking - it says the float should be 28-30mm above the plate level when the top plate is held upside down at an angle of 30 degrees to the horizontal. I made the measuring card they suggest.


Mine was a good 5mm or more above 30mm. There's no adjustment - the height is governed by the needle valve. I took the needle valve out and compared it to one that I removed when servicing a carb on a previous occasion. The one in this carb (on the right, from a recent rebuild kit) is clearly longer by a few mm, which means the level of fuel in the float chamber will be ~5mm lower.


I doubt that 5mm is worth worrying about, but since the one I had spare still seemed to be in serviceable condition, I swapped it over and was able to get the float to sit between 28 and 30mm. It still seals nicely when the valve closes.

[CJH]

With a new pull down unit (one of Brickwerks' finest - OK, second finest, they're out of stock of their finest and anyway I couldn't justify the extra £53), I adjusted the choke settings.

First of all, use a rubber band to mimic the tension of a cold choke spring, then operate the throttle to set the fast idle screw onto the top step of the cam.


The choke flap should be closed at this stage. (And yes, thanks to this photo I've just noticed that the flap isn't perfectly square in the hole).


The instructions say to then push on the end of the pull down unit's adjuster screw to open the choke flap, but I used my vacuum pump to operate the pull down. Check the choke flap gap. The instructions say that this 'H' variant carb should have a gap of 2.5mm +/- 0.2mm. They advise using a twist drill to measure the gap. Here I noticed a potential problem from the 'lash' in the choke lever part that I've made - it manifests as a variable gap in the choke flap. I reasoned that air flow would pull the flap open as far as it would go and take out the lash, so I measured the gap at it's maximum value. To adjust the gap, turn the screw in the end of the pull down arm.


A pre-condition for this adjustment is that the end stop arm is adjusted properly. The arrowed gap in the next photo should be 0.5 - 1mm apparently. If it's too different from that you may not be able to get the choke flap gap correct. To adjust the gap, bend the metal arm to the left of the gap in the photo - push it left or right to adjust the gap.

[CJH]

Then I adjusted the end stop for the second stage throttle. That maintenance manual referred to a special tool (I think a dial gauge to check the flap movement), but the VW factory manual helpfully says to just wind the screw till it's touching (use a piece of thin paper to detect that point) then wind it a further quarter turn. Then secure it with paint - I used threadlock. The manual says to open the main throttle and wedge it open - that's the screwdriver in the photo. The rubber band you can see in the photo is to hold the second stage throttle closed while adjusting the screw.


Finally, the VW manual says that the gap either side of the 'locking lever' (that's the short arm of the other part that I've made) has to be 0.4mm +/-0.15mm. They advise to just bend the arms of the u-bracket to achieve this. Mine was way off. Here I noticed that the swept-up shape of the original part helps here because it's nearer the ends of the arms, but it's not difficult with the lever where my new part has it.

Before:


After:


Right - that's it. That's as much as I can adjust off the engine. It now has to go back on to have the idle mixture set, the idle speed, and the fast idle speed. If it doesn't work then I'm going to give up.

[kevtherev]

In a way this is more enthralling than an MM restoration thread
I ❤ pierburgs

[CJH]

I ❤ pierburgs

I agree - there's a charm to an old-school carburettor. I'd like to think this one will run at least as well as my 'normal' carb now, but unfortunately that isn't so good at the moment. Maybe it didn't like being swapped out so frequently just recently. My engine was running so sweetly just a few months ago, but just recently it's stalled a couple of times when idling warm, has a bit of a wobble at idle, and the cold start/fast idle isn't working the way it used to. I've identified the leaky pull down unit which should explain the cold start, but the warm stalling is a mystery at the moment.

I've changed all the ignition parts (amp, coil, plugs, leads, dizzy cap and rotor), and the timing is spot on. I'll check the dizzy vacuum unit next time the engine cover's off. I stripped, cleaned and lubed the dizzy a few months ago and it cleaned up the idle wobble no end - worth checking it over again I guess. My leaky head seal seems to be 'progressing', to the point that the number 1 and number 2 plug recesses were a bit gummed up - I guess I should clean them out properly in case the spark is jumping occasionally. If that and the refurbished carb don't fix it I may be looking at tappet adjustment and a compression check I guess.

[CJH]

Aargh - what a numpty. I just went out to check the dizzy vacuum unit, and noticed that I'd forgotten to refit the bung over the second vacuum spigot round the back of the carb - the one next to the dizzy spigot, and which I've disconnected from the air filter housing. That should fix the rough idle and warm stalling I think.

Oh, and the dizzy vacuum unit won't hold a vacuum either - it responds to an initial vacuum, but gradually relaxes unless the vacuum is continually pumped. Again, not too much of an issue yet, since the engine will effectively 'pump' the vacuum continuously, but again, a leaky vacuum system is a bad thing. Time to try out that 'almost right' vacuum unit that I bought at Busfest last September.

Once those bits are fixed I should have a decent benchmark against which to compare the fully adjusted 'test' carb.

[Mocki]

so now you are getting to be fully at home with these setings, how much do you want to refurb and set up one of mine??
i really dont seem to have the time and i havent got my head round these settings you have so carefuly documented.... lol

[CJH]

Haha - watch out Bromyard!

I'm flattered by your confidence in me, but I'm not sure I'm up to that - it's one thing tinkering with my own test carb, it's quite another taking money from someone else. I don't have the tools (like a gas analyser) to get it right by the book, and to be in any way confident that it works properly it'd have to be tried on my own van. That's a fair bit of work. And I've no idea yet whether anything I've done to this test carb has made a difference. I might think again if this one turns out ok though.

This morning I swapped the leaky dizzy vacuum advance unit for a Powerspark unit (this one I think) that I bought at Busfest. I was told by the salesman on the stand that the vacuum advance curve is very similar to the correct unit - a few degrees out he said - so I thought I'd give it a go.


I also swapped the leaky choke pull-down for a new one. To do it in-situ you definitely need to remove the choke, and setting the correct choke flap gap is almost impossible thanks to the position of the second stage throttle diaphragm.

I also put a bung over the unused carb vacuum spigot.

The result - it fired up first time from cold, ran unevenly for a few minutes then settled down to a nice smooth idle. The choke flap gap was clearly wrong - virtually closed at first - and the fast idle didn't seem fast enough, so that might explain the initial uneven running. I'll set that up properly when it's on the bench. I haven't driven it yet but I'm happy that the smooth warm idle is back.

So that's my 'normal' carb to use as a benchmark. Then I'll swap in the 'test' carb that I've done all the adjustments on - moment of truth.