Pierburg 2e3 - no fast idle

[Zebedee]

I've just replaced the weber 34DAT on my '88 caravelle with a rebuilt pierburg and have spent a while tuning it.
When cold the choke flap is nearly shut and has a gap of about 3mm. It starts first turn of the key but tries to idle at 900 revs - there appears to be no fast idle at all.
When its warming up the choke comes off as it should and it'll idle at 900 revs without a problem. I've set the CO up with an exhaust analyser at 1.5% at idle when warm.

Any idea why theres no fast idle?

Other than that it runs much better than with the weber. Seems to have loads more power pulling up the hill near our house in 3rd instead of needing 2nd.

[Iridium]

There's a fast idle screw near the base of the carb which is quite fiddly to reach. This must be turned until the fast idle is up to 2000 rpm whilst on the second highest step of the auto choke step cam. Best to take off the airbox intake from the carb to firstly see this screw and secondly to reach it. Engine must be warmed up.
I had the same prob myself. 1.9 DG.

Regards,

Iridium

[Zebedee]

There seems to be a tamperproof cap on that screw which I can't remove. Wish I'd taken it off before I fitted the carb now.

[Novice in need]

Isnt that the mixture screw (with tamperproof cap on)... the idle speed screw faces directly at you when looking from the back on a Pierburg 2e3. How did you correctly adjust the mixture (CO Reading)with a gas analyser if you wasnt adjusting with the mixture screw in the first instance?

[Iridium]

Zebedee,

you're absolutely right, originally the fast idle screw had a tamperproof cap and obviously your one still has.
Fast idle adjustment is like this:

Warm the engine to normal running temp.

Make sure the idle speed and mixture are o.k.

Turn off the engine.

Unbolt the air filter from the top of the carb and place it clear (you may already have done this if idle speed and mixture are wrong.) Keep the vacuum tubes from the air box to the base of the carb connected.

Turn the fast idle stepped cam so that the fast idle screw is positioned against the second highest step.

Start the engine without moving the throttle.

Adjust the fast idle screw 'til you reach 2000 rpm with an allowance of 200 rpm up or down.

Tamperproof plugs are easily broken off with a screwdriver. Adjusting will require a short thin screwdriver and patience.

Iridium.

[Zebedee]

Cheers.
Idle and mixture are now correct (its just been checked on an MOT emissions type machine while i was getting my LPG install checked).

I tried what you suggested and on the 2nd highest step it idles at about 2100rpm. When cold it idles at 900revs on choke.
Think i'm gonna start again, set the choke gap then have another go. Maybe thats not correct.

[Iridium]

O.k.

Give us a nod whatever the result.

If you do have more probs. I've got a feeling it may be that the fast idle cam is not springing round when the engine temp is cold. Therefore the bi-metal strip may be disconnected.... or a host of other things.

Good Luck.

If its any consolation I did a lot of head scratching with my carb and now it's bang on.

[Zebedee]

I reset the choke gap to 3mm ish. It was at about 1mm before.
Warmed it up to normal operating temp. Switched off and put the fast idle screw on 2nd highest step. Started engine and it revved at about 2000 revs.

Tried it this afternoon when it was cold again and it tried to idle at 900.

Not got the foggiest whats going on.

[Zebedee]

Still not got this to work properly.
Its running on LPG now and i've come up with another problem.

It still idles at 900 revs on petrol or gas when cold (even though it runs at 2000 when i run the test with the fast idle cam on the 2nd step) but when its up to temperature it'll idle at 900 on petrol but the revs raise to 1300 if its running on gas. No idea at all whats going on now.

What are the symptoms of a duff choke pull down unit?

[kevtherev]

The fast idle is set by depressing the throttle once before starting and not using the throttle while cranking
are you doing that?

[kevtherev]

For adjustments to this part of the carb it must be removed, along with the bi metal spring and housing

1/. Adjustment of fast idle cam must be done using a vacuum pump mechanism to the 2nd stage choke and create a vacuum around 300 Millibar
2/. Open the throttle , to freely move the cam.
3/. Gently move the lever (c) or the dog in the bi metal spring housing, clockwise and then release the throttle valve.
4/. Check the distance (x). It should be 0.2 - 0.8 mm.
Adjust the value using distance lever (d)



With carburettor off "set" choke as normal (manually) the throttle stop screw A should sit on top of cam lobe 1, once the throttle shaft is moved it should drop to cam lobe 2.... then when the carb is on the engine the coolant temp will move it down the cam progressively .

Further refinement can be found using screw A when engine is HOT and at working temp adjust screw A to final cam lobe 4 to just touch the surface of lobe.

how it works
As the throttle opens and the stop (A) opens.. the bi metal spring in the auto choke puts pressure on the dog (C) moving the cam (lobe 1) over the stop..
The electric heater in the choke then acts on the bi metal spring and as soon as the accelerator is touched the cam lobe moves to the next step
Some times the springs will weaken and need re tensioning

[kevtherev]

What are the symptoms of a duff choke pull down unit?

over fuelling on acceleration.

The pull down unit opens the choke under acceleration during warm up.

[Zebedee]

Choke works fine. No over fuelling so i assume the pull down unit is OK.
Press throttle once when cold and the choke sets with 3mm gap, and comes off within a few minutes at the temperatures at the moment.

Fast idle cam turns round when throttle is also pressed but doesn't get to the highest step (1 on your piccy). It gets to 2 i think.
When the engine is warming up the cam turns round as it should but as it starts at 2 anyway it only moves a little way and doesn't lower the revs as its at 900rpm anyway..

The haynes mentions removing the choke body and gasket to set choke gap. Does that mean the whole of the of the choke housing need removing to set it and the choke flap gap? One of the screws has a knackered head so it'll need drilling out if it does.

When the fast idle cam is set where it should according to mr haynes it revs at 2000 as it should. It just doesn't get that far around to get to the right place when the pedal is first pressed.

[kevtherev]

Choke works fine. No over fuelling so i assume the pull down unit is OK.

does the flap open OK when you rev the engine?

Press throttle once when cold and the choke sets with 3mm gap,

no.. seting the choke is automatic, when you press the pedal it sets the fast idle cam
...there is only a 3mm gap when the engine is running

Fast idle cam turns round when throttle is also pressed but doesn't get to the highest step (1 on your piccy). It gets to 2 i think.

When the fast idle cam is set where it should according to mr haynes it revs at 2000 as it should. It just doesn't get that far around to get to the right place when the pedal is first pressed.

slacken the three screws holding the housing on
Rotate the housing 1/8th clockwise
depress the accelerator fully and note the position of the cam
try another 1/8th turn if it still misses the top step... and so on

do you get that?

[Zebedee]

does the flap open OK when you rev the engine?

I haven't checked if the flap opens when i rev the engine.

no.. seting the choke is automatic, when you press the pedal it sets the fast idle cam
...there is only a 3mm gap when the engine is running

Theres a 3mm gap with the engine off at the moment. So it should be completely shut when the engine is off then?

If its only supposed to have a 3mm gap when the engine is running then i think i'll need set that up too.
The haynes manual says: "Open the throttle and position fast idle adjusting screw on highest step of the cam. Push vacuum diaphram pullrod towards vacuum unit. Hold pullrod in position and use adjusting screw to get specified choke flap gap (3.3mm +/- 0.2mm)" which sounds simple enough.

slacken the three screws holding the housing on
Rotate the housing 1/8th clockwise
depress the accelerator fully and note the position of the cam
try another 1/8th turn if it still misses the top step... and so on

do you get that?

I'll give it a try tomorrow and see what happens.