Club 80-90 Forums

Ok, i know a little about engines and carbs but not loads. We have a 1986 1.9 petrol T25, our solex had worn out so we had a weber convertion kit from justkampers fitted (think its a ADGAV).

After changing the HT leads, vacuum hose ignition coil and spark plugs the engine remains the same, when first started it idles way to low and the whole engine rattles before stalling. however once its off choke it runs absoloutly perfect, with the idle speed sounding just right. I suppose im after general advice of things to try but i was also wondering if there was a way of setting the "choke on" idle speed slightly higher, without changing the rest of the settings, and if so which screw do i turn! An option is to take this to a proper tuner and get it done for £60, but the new carb/manifold/labour already cost us £450! Thanks for any advice!

Hi,

I have a 1.9 Watercooled Petrol which came with a Weber 34DAT carb. This is the listed Weber replacement for the Pierberg 2E3.

If yours is one of these I can help you, and have details of setting up this carb

Basically with carbs of this type (34DAT) when you press the accelerator to the floor prior to starting it from cold a bimetallic strip closes the choke flap. There is a setting screw to set how much fast idle you get with the choke flap in its closed position HOWEVER an additional adjustable mechanism is attempting to open the choke by utilising engine vacuum, which gives an initial choke opening.

In my case it was the setting of this adjustment that was the problem, and the choke was being opened prematurely, which meant that fast idle was slower than it should be, with similar results to yours.

As soon as you start the car the bimetallic strip starts to get warm and begins to open the choke flap anyway.

So then .......Identify the carb, perhaps supply a photo of it and I may be able to tell you more.

Regards

Dave

Hi thanks alot for your reply, i have looked and although it is hard to see im sure it says 34 DAT 11 on the carb.



Picture of the overall engine:


There is a photo, i have labelled the three screws i can see in the hope it would make it easier to explain, i do not know what each of these do apart from "2" this just sets the idle speed by applying throttle i think.

What you where saying about the fast idle speed was what i was hoping would be the case, basically i think i just need to increase the idle revs when the engine is first started, but leave the revs as they are once the engine is warmed up and the choke is off ( what you described in a more technical way i think) Thanks Dave!

Hi,

Yes, its a 34DAT. Good !

Screws are, looking at your first picture, and starting at the lower arrowand working upwards.....

Lowest arrow - corner of carb - mixture screw
Middle arrow - idle speed screw
Upper arrow - choke opening adjusting screw - when engine running and vacuum available

Remove the air filter housing on top of the carb - three screws at the top of black plastic cover.

Once removed and as you look down on the carb you will see another screw. The pointed end of this screw will be disappearing into the bimetallic strip housing which is the cylindrical housing fed with two rubber pipes vertically above the idle speed screw. Its flat screw head is pointing away from you so in other words you will have to come at it with the head of a thin flat screwdriver pointing towards you.

This screw bears against the choke cam, which has three or more steps on it and sets up increased engine speed when the engine starts initially. If you say turn it clockwise say 1/2 to 1 turn (Clockwise means as you look at the slot in the screw which is pointing away from you - You would be facing towards the back of the carb) this should increase the fast idle. Now replace the top cover and give it a try.
(Of course you can only carry out the adjustment when the engine is cold, typically once a day, so that it gets a bit of a pain.

Don't forget to put the accelerator to the floor and let it up so that the choke is set.

IF IT DOESN'T make the difference you expect then come back to me and we will take the next step. As I pointed out it may be that due to a setting when you initally start the transporter, the vacuum is pulling the choke more open than it needs to be, which has the effect of reducing the fast idle, but as I say lets wait and see.

Trusting this helps

Regards


Dave

Top man! i'll give it a go tomorow, why do you say this can only be adjusted once a day? And just to confirm, i have been doing this anyway but more by fluke, you should always press the accelorater once before starting the engine? Or do you only do this to set the choke when its cold?

I can tell u've been in the same mess were in now, here to sorting it!

P.S. i knew the numbers on my arrows where far to small!

Hi,

I have suggested once a day to make sure that the engine is cold.
Remember that as soon as the engine is started, the water being circulated around the bimetallic strip housing is starting to warm up and the bimetallic strip is getting warm which is opening the choke. As the choke starts to open, the cam turns with it reducing any fast idle.

I typically might start my car cold at say 1pm - using the foot to the floor and return method to set the choke. This allows the choke flap to shut.
I might start it again at say 4-45pm and typically not use the choke since it will start without. That's how mine functions at the moment.

I would suggest that you only adjust the back screw I have identified for you to see if it is only this setting that is causing your problem. Certainly leave the other three you have identified alone, until we know the outcome of your one turn on the rear screw. Remember, clockwise as though you were looking at the screw head.


Regards


Dave

Hi,

Any Luck ? - am on line now !

Off line at 10:53 am

Regards

Dave

Ok so went out at 11:00 today, hopefully have another chance around 4:00. So i adjusted the screw and went clock-wise one full turn, pressed the pedal to set the choke, gave it some revs for a few seconds and it idled but was not quite happy still a bit jumpy as though it was mis-firing (it always does this but it was doing it a little more) I thought i may aswell just let it run and gradually let it come of choke itself, and about 3 minutes in the engine wobbled alot and stalled, i assume it rolled of another cam. Will try going anti-clockwise half a turn and see if that helps.
Heres the screw i turned for anyone else in the same situation(this is before the screw was turned):


While i was pottering i noticed two things,

This braided pipe is moist at the bottom and the filter housing only has locations for two screws the third screw is misalligned (third screw glued in by the mechanic that fitted it!) would this be letting too much air in if its not screwed down tight? Anyway if these two thinghs have nothing to do with the carb misfunctioning ignore them.

Its frustrating that it was idling fine then stalled as it gradualy warmed! Just to clarify i went clockwise from the point of view of the first picture, thats right yeah?

Hi,

Regarding the braided pipe. Take it off and make sure it isn't porous. To check it ,block one end of it, and attach your mouth to other end and blow.
It's more exciting if you have the pipe under water. If it is porous it will play havac with your mixture. The pipe by the way takes vacuum from the inlet manifold and applies it to the brake servo via a non return valve.

Re the screw - Yes, you have turned the screw correctly. Can you see the screw tip bearing against the cam ? I would not turn the screw back just yet.

I would ask you to Turn screw 3, 1 turn ANTI CLOCKWISE (As you view the screw and try it again.) This adjustment opposes vacuum opening the choke flap, and sets the initial air gap.

Yes, one screw which clamps black plastic housing does not tie up with a threaded hole.

If you want to have a word on the phone then please ring me , I shall be here untl 3pm.

Regards


Dave

ok! just took off braided pipe, the one way valve works fine but the braided hose has maybe ... 20 tiny holes in it! will try a section of hose pipe on a temp basis dont think anything but air goes down there does it?

Tried what you suggested and give both screws 1 and 3 a full turn anticlockwise, still stalled in the same way after about the same amount of time but seemed to do it gentler.

Would i be right in think there isn`t much point in messing around on settings untill the pourous pipe is sorted? Once the pipe is sorted would you have anything else to reccomend. The choke screw is still in the same position it was (half a turn clockwise from original position)

Thanks for your patience!

Hi,

Yes, you should replace the pipe first as a matter of urgency, since it is leaking air into the inlet manifold.

Once you have done this ................................

Find someone to help you with the next bit, so that you can observe what is happening at the carb end of things.

Remove the plastic top, and leave it off. Whilst looking in to the choke barrel you should find the flap is open.

Ask your helper to put the accelerator to the floor and let it up again. You should see the choke flap close COMPLETELY with no gap at all.
Now go back to the rear screw and add 2 turns onto it.

Once you have done this ask them to start the car . As they start turning it over with you looking directly over the top of the carb you should see the choke flap open slightly. Estimate how much the bottom of the choke flap is away from the edge of the barrel in which it sits as the engine is being turned over. Estimate this in m.m.

You will now know if the extra turns at the rear have helped, and you need to report back what you have found and seen.

Some general comments

If the engine is running O.K. once warm, leave the mixture screw alone. You would only adjust this when the engine was up to temperature anyway.

Your problems are basically associated with the choke settings.
Some of the information I have from Weber is unfortunately in Italian, but the diagrams are clear regarding what is required.
The documentation assumes that a vacuum supply is available and also that you are in a position to make measurement of flap distances both at the throttle and choke positions, which really implies that the carb is off the car.

You will appreciate therefore that assuming you haven't got these things, we are having to get ourselves into a position whereby a setting we change makes a difference, better or worse and then proceed accordingly.

Basically the above check will indicate what difference the extra two turns of the rear screw have made, and this with the gap you will have seen indicates what to do next. It is sensible for us to only change one thing at once for obvious reasons.

I left my telephone number for you for a short time in a previous message, before editing it out. If you wish to know more please use it and ring me.
It is quite difficult to describe some of this information in text when I could do it in a two minute phone call. It is Sunday evening now so as I say feel free to ring me, I think it will help.

Regards


Dave

Hi,

Just some thoughts that I have had.

(1) You should have been supplied with the carb fitting instructions - these will give you warm idle mixture adjustments. They contain nothing about setting the choke or fast idle adjustment, but do state that engine idle speed should be 900 rpm. The mixture screw is adjusted in conjunction with the idle stop screw to get the highest revs but you limit the revs to 950 rpm using the idle stop screw . Once you have attained the highest revs you screw inthe mixture screw clockwise half a turn clockwise which should set the CO to about 1.5 and cause the revs to drop to around 900rpm.

I mention this since replacing the vacuum pipe may have an effect on how your engine runs and a mixture adjustment may be needed when the engine is warm

(2) My problem was similar to yours. That is, lack of fast idle at startup. I found that the rear screw which you have adjusted, increased the choke fast idle very little, but that the choke pulldown adjustment - your screw 3 did make a difference. I have mentioned that when the engine starts choke pull down takes place because of engine vacuum and gives some initial choke opening. The amount of choke opening you get with vacuum (ie at startup)is controlled by screw 3. From memory as you screw 3 in clockwise, vacuum is resisted more and therefore you would expect the cam to stay on its highest lobes and stay on fast idle. Turning screw 3 anti clockwise has the opposite effect and causes spring pressure to assist vacuum in opening the choke flap. Since the choke flap is linked to the fast idle cam then fast idle reduces.
NOTE : I have just had a look at your photos. Start off by uncrewing screw 3 by say 1 turn and see its effect.

(3)In the previous e-mail I gave you some checks to carry out so report back and we will see what you are finding.

Regards


Dave

Well i havn't really been able to do much as im after the inlet manifold pipe the braided hose thats pourous, where did you get yours from? Is it this?

http://www.justkampers.com/shop/type_25 ... -pipe.html

Once i have this i'll condense what you have wrote above and have a proper look at it!

Hi,

After finding the fault, I used a piece of standard pipe to keep me rolling. I will come across a piece of vacuum pipe at some stage.

The one I have replaced looked exactly like the one in your photograph, and I would expect it to be straight but reinforced for vacuum use.

Regards


Dave

Sorry, hope you dont think iv'e gone cold on this subject, ive been really busy this week, amongst other things some woman drove into my car while it was parked! I'll do the above checks at wkend