Pierburg 2E3 choke

[kevtherev]

The vacuum comes from the venturi and is constant.
That's why the second throttle is controlled by the gate.
I too have noticed a gap, even at rest the second butterfly is not completely sealing the venturi.
IIRC I posted a picture up of that.
I have chased this lumpyness/hesitation for ages, I'll be removing it this weekend to take a look at the transfer jet mechanism again.
I also have sealed the gaskets, both between the half's and the isolator gasket.

Next step for me also is the brake booster, and whether that has a leak.

[itchyfeet]

Have either of you tried changing the bypass valve
they can't last forever.

[CJH]

Have either of you tried changing the bypass valve
they can't last forever.

In the brake vacuum hose you mean? No I haven't, probably should at some point, but I know that my 'normal' carb runs fine on all the same pipework.

Or are you referring to a different part?

[itchyfeet]

I mean electrical cut off, when I changed mine for a second hand one it, or the gasket clean up helped alot indicating airleak from one or the other.
clicking does not to me indicate is works ok

[CJH]

Ah, ok. No - haven't changed that, or even attempted to remove it. I've read they can be difficult to remove, with the body perhaps separating from the threaded part.

[CJH]

Yikes - part number 052129413A : £71 from VWHeritage. I'm not even going to risk breaking it if a new one costs that much. Is there a way to test whether it's working in situ?

[itchyfeet]

Swap the one from your known good carb?
usual test is does it click but surely that doesn't tell you if it's fully working.
Asfar as I know it allows air in to help stall tge engine at switch off.

[CJH]

Swap the one from your known good carb?

You mean risk breaking both of them? I think I might first try and trace the pathway to see if I can 'non-destructively' determine whether it's opening and closing.

[CJH]

Actually, I've got a 'parts' carb that I could take one from to test. Am I right that they screw in, and there's only the cylindrical body to grip (i.e. nothing to get a spanner on)?

[kevtherev]

Yes screw in, I only have one spare too

[CJH]

Actually it looks like it cuts the fuel/air mixture, rather than letting air in. So a quick check would be to remove the power to it from an idling engine - the engine should die. But of course that doesn't check for air leaks.

[itchyfeet]

Actually, I've got a 'parts' carb that I could take one from to test. Am I right that they screw in, and there's only the cylindrical body to grip (i.e. nothing to get a spanner on)?

There is a lug on it which you can use to stop a spanner slipping around.

May be a red herring but it's good to go through the possabilities. Never had the duct heater out either.

[CJH]

Never had the duct heater out either.

I don't think that's a potential source of air leaks, as it's just a contact heater. The heater itself sits against a brass insert in the throttle body.


I removed the cutoff valve from my 'parts' carb this evening. After a cleanup it seems fine. I learned a few things.
1) The threads were a bit corroded, making it difficult to remove. If moisture can get in to corrode the threads then I think air could get in too, as it's not a taper thread. I doubt it would be much though.
2) The rubber seal on my parts carb is brittle and cracked so is definitely not air tight. The valve screws in until the brass tip is tight against the end of the recess in the throttle body, so it's not possible to tighten it further against this rubber seal. Once the seal shrinks and ages a bit, it won't be under compression. Neither of the carb refurb kits I've used have had this seal so I'm not sure how you'd get a new one. Perhaps a bit of PTFE tape around the threads would make a good seal instead.
3) The 'click' comes from the internal plunger, inside the brass tip, moving under the magnetic field. I'd say that if you can hear a click then the only moving part is, well, moving.

[CJH]

I removed the test carb from my van this evening in preparation for stripping it down and checking everything this weekend. The idle cutoff valve came out fairly easily and looks ok. But the rubber seal is worse than the one from my parts carb.



So, belt and braces, a couple of turns of PTFE tape around the threads and a couple of 10mm O-rings should make an airtight seal.



But I suspect I may have discovered the problem when I removed the carb from the manifold. Both sides of the spacer/gasket combo below the carb were wet with petrol. If they had been making an airtight seal they ought to be dry, so I suspect they weren't sealing properly. So I'll make a couple of fresh gaskets out of thick gasket paper and put one either side of the spacer - the extra thickness should help to lift the accelerator pump lever clear of the manifold. I'm undecided about using a sealant - I'd prefer not to so that they can be removed easily.

[itchyfeet]

made a fresh gasket with 0.4mm gasket paper this week too, just greased it, no other sealant, test drive tomorrow