Pierburg 2E3 Issue: Stuck on High Revs

[jamesakers]

Problem: When warmed up and after hitting a certain speed the revs stay ridiculously high. Touching the throttle makes no difference. The only way to stop is to turn the engine off and restart.

This all started because I noticed the Pierburg 2E3 was leaking so purchased rebuild kit. I read as much as I could beforehand but still made mistakes. What i've done so far:

• - With carb removed I found there was no gasket at all between the carb and manifold
  - Split and cleaned the carb, replaced the enrichment valve diaphragm and 2 main gaskets
  - Replaced the vacuum pipes connected to choke pull down and stage 2 diaphragm (did not check if they held vacuum :S)
  - Noticed the vacuum pipe from carb to air box had melted at the end so cleared the blockage by cutting the pipe

Once i'd refitted the carb the van ran really lumpy and was clearly not happy. After driving it round the block the revs got stuck really high and would not come down.

I re-read all the posts and found CJH's mention of the air intake vacuum so I remelted the pipe and the engine ran much less lumpy. (It must have been melted by a previous owner to improve things).

Next, I tested the vacuum pipes by sucking on them to see if they worked; stage 2 diaphragm and dizzy vacuum worked fine but the pull down unit did nothing. I could suck air all the way through. To check for any other air leaks I sprayed carb cleaner at various places on the carb, here is a video of me spraying the pull down unit, you can hear the change in engine noise:

YouTube video: https://youtu.be/DPNni8kve5w

I ordered a new pull down unit from Brickwerks.

Further reading of Pierburg 2E3 posts and I found out about the tiny restrictor valve inside the pull down unit vacuum pipe. Luckily I keep everything I remove from the van so split open the original pipe and found it.



It was clogged up and needed a good clean. I inserted that into the new pipe, fitted the new pull down unit and set the choke flap to the correct opening.

This is the split in the original pull down unit:



Because I did not check if this was working before messing with the carb i'm unsure if I broke this by running the engine without the restrictor in place or whether it's been like this for ages (the blocked valve suggests it has).

Started up the engine again and it's running like a dream, no air leaks or lumpy running.

BUT...

When the revs hit a certain point they still stay there and only an engine restart cures it. I seem to have fixed all issues apart from this one.

Any ideas what it could be?

I'm going to take the van for a run tonight and when the revs get stuck i'll remove the pancake and photograph/video what is happening.

[CJH]

I wonder if the end of the lever that operates the enrichment valve is binding on the top of the inlet manifold. I had this problem, and it meant that the cam on the end of the throttle shaft could get trapped behind the lever and jam the throttle open. There was a brief discussion of it here. I didn't take a photo but Itchy did:

.

The end of the lever on my original carb had been trimmed to solve this, but I think a good clean of the top of the manifold would fix it. The depth of the spacer betwen the carb and the manifold seems critical to avoid this.

[CJH]

Because I did not check if this was working before messing with the carb i'm unsure if I broke this by running the engine without the restrictor in place or whether it's been like this for ages (the blocked valve suggests it has).

Running the carb without that restrictor won't do any harm I think - it just damps the action of the pull-down unit I believe. Total pressure won't be changed so it can't be the reason for the split diaphragm as fas as I can see.

[itchyfeet]

The only way to stop is to turn the engine off and restart.

Thats odd, trying to think what changes after restarting other than vacuum
are you sure you have the second barrel actuator vac pipe conneted to the right place?

[itchyfeet]

oh hang on you didn't put that restrictor in the second barrel actuator pipe by mistake?

[jamesakers]

The end of the lever on my original carb had been trimmed to solve this, but I think a good clean of the top of the manifold would fix it. The depth of the spacer betwen the carb and the manifold seems critical to avoid this.

OK, I'll check that this evening.

The only way to stop is to turn the engine off and restart.

Thats odd, trying to think what changes after restarting other than vacuum
are you sure you have the second barrel actuator vac pipe conneted to the right place?

Yes I think so, it's connected to the one right next to it on the carb.

oh hang on you didn't put that restrictor in the second barrel actuator pipe by mistake?

No, it's in the pipe connected to the pull down unit.

Could it have anything to do with the enrichment valve I replaced?

[itchyfeet]

check the pipe is clear, it has a restrictor in it.

[jamesakers]

check the pipe is clear, it has a restrictor in it.

Thanks Itchy, i'll check that as well later.

This is a video I took before replacing the pull down unit: https://youtu.be/cAEMhlILu58" onclick="window.open(this.href);return false;

The choke step down appears to be working OK when the accelerator is depressed.

[jamesakers]

Here are some videos I've just filmed of the problem:

Engine stuck on high revs: https://youtu.be/6O6foXx3_Fk (cam looks fine)

Looking down the barrels when stuck: https://youtu.be/NBipxaTe45k

Engine restart resets it: https://youtu.be/_yQqtYNwGuw

I sucked on a pipe connected to the carb where the stage 2 goes in and it's not blocked.

[jamesakers]

I've just looked through my pictures and think i've found the issue:

The Throttle Body Heater and Choke Heater plugs are swapped over.

I'll test this evening to confirm.

[itchyfeet]

I've just looked through my pictures and think i've found the issue:

The Throttle Body Heater and Choke Heater plugs are swapped over.

I'll test this evening to confirm.

Should not make any difference, they are both heaters switch from the same thermoswitch circuit.

[jamesakers]

Should not make any difference, they are both heaters switch from the same thermoswitch circuit.

Damn.

[jamesakers]

So I checked the wiring. I had the Throttle Body Heater and the Choke swapped over. This meant that the coil in the choke stopped getting power when the thermostatic switch turned off meaning it wouldn't open all the way to come off the last step. It also meant the Throttle Body Heater was permanently on.

The choke now comes all the way off BUT the issue getting stuck on high revs still remains.

[CJH]

Here are some videos I've just filmed of the problem:

Engine stuck on high revs: https://youtu.be/6O6foXx3_Fk (cam looks fine)

Looking down the barrels when stuck: https://youtu.be/NBipxaTe45k

Engine restart resets it: https://youtu.be/_yQqtYNwGuw

I sucked on a pipe connected to the carb where the stage 2 goes in and it's not blocked.

Looking at the second video, there seems to be a fair amount of fuel dribbling down the stage 2 venturi, even though the stage 2 valve appears to be closed. I don't really know if this is normal, but I'd have thought the fuel should only be drawn up when there's a significant vacuum, and with the valve closed I can't see where that vacuum would come from. The image below from this document shows how the stage 2 throttle should work.



It's not clear in the video where the dribbling fuel is coming from, or whether the valve is in fact cracked open. I can't decide whether the dribbling fuel could be a *consequence* of the high rpm (with a bit of vacuum created because the valve is cracked open), or the *cause* of the high rpm (valve open when it should be closed, causing a vacuum that draws the fuel in).

But, one thing you could check (which I don't think I can see from your videos): the second stage throttle valve should be locked closed until the primary throttle valve is fully open - there's a plastic interlock part, the white part in the centre of this photo (not the circular anti-tamper screw cap top-left):



If yours is cracked or broken it's possible the stage 2 throttle valve is opening more than it should while the stage 1 throttle is still closed. Worth a check.

[CJH]

Looking again at the video, the dribbling fuel definitely seems to be coming from the main diffuser, rather than the transition system. I'd have thought there needs to be a significant vacuum to draw that fuel up.