When I got my 1990 Mk2 Polo 1043cc Fox I thought I would change the automatic choke on the Pierburg 1B3 for a manual one. However the kits available at the time (Sandalloy / Mafco) were around forty pounds and didn’t seem very well made. Looking at a Haynes manual I noticed that the Vauxhall Nova 1.2 and 1.3 used a Pierburg 1B1 from around 1982 to 1992 and had a manual choke as standard, so off I went to the scrap yard and returned with a choke unit for a fiver.

This is a picture of both sides of the manual choke.

The black device at the left of the bottom image is a vacuum diaphragm, when you start the car on full choke as soon as it starts the diaphragm rod pulls the choke off slightly. (Choke pull down) The original automatic choke had this device as well.

This is a picture of the choke unit separated.

The spring you see arrowed red in the top part is a bimetallic spring . When you pull the choke knob the choke flap is closed via the tension of the spring, but if you forget to push the choke back in the spring expands in the increasing ambient temperature and opens the choke flap up for you. The piece arrowed blue acts to limit the amount the choke flap closes due to the action of the spring which also makes sure the choke is off when you push the choke knob back in.

This manual unit fits straight onto the 1B3 carb but I needed to alter the linkage from the choke flap to the choke unit, easily done by making a new one out of welding rod. Also the arm that contacts the fast idle cam needed adjusting / bending so that it made contact properly. I did this by cutting and welding but if you got the arm off the carb from the Nova I would think that you could just swap them over.

This is a picture of the carb minus the choke unit with red arrows showing where to alter.

This is the carb complete with the choke. The red arrows point to the three screws to loosen so that you can rotate the choke which has an effect on the choke flap but is normally set so that marks on the choke cover and carb body align.. The blue arrows point to screws that adjust the fast idle. The original choke cable I think was a solid single wire so that when you pushed the choke knob back in the choke mechanism would open in a positive manner. I am using a stranded cable so I added a spring, its end can just be seen arrowed green. This pulls the choke mechanism open fully when you push the knob back in.

On the dash in the car there was a blanking plate where the choke knob must have gone in earlier model Polos. This is easily removed but left a hole too big to hold my choke cable assembly so I had to make a plate to cover it and drill a hole in the plate for the cable to fit correctly.

When removing the automatic choke unit you need to take care of the two 13mm pipes that feed coolant to it which I did by connecting the two ends of the pipes together with a piece of solid bar.

I think this is a vast improvement over the automatic choke that was fitted before and this modification has not given me any trouble in nearly 10years.

Edited 6 March, 201016 yr by William24

Thanks for a really nice article mate. I've pinned it up.

brilliant, would i have this carb in my 88 1.3 cl?? if so think i may do this as i hate auto choke on my mk2, the manual on the mk1 is 1,000,000 times better,

thanks

The '88 1.3 engine has the Pierburg 2E3 carb. I am not sure that the manual choke unit off the 1B1 carb will fit as easily as it does onto the 1B3 carb that the 1043 engine has.

:( i need manual choke

Another area where there might be some unreliability with the Pierburg 1B3 is the idle speed. This is controlled in part by the No 82 relay/control unit (above the passenger footwell) that detects via an electrical signal when the engine idle speed drops below approx 700 rpm ( maybe when under increased electrical load for example ). It then sends electrical power to the two way valve on the bulkhead which then adjusts the idle circuit on the carb via a small vacuum pipe which goes to a special type of idle speed adjustment screw which finally brings the idle speed back up.

This sort of control is not really needed and if something goes wrong it can be hard to track down where the problem is.

If you are in the scrap yard getting the manual choke unit you can also get the bog standard bypass idle adjustment screw off the 1B1 carb from the Nova at the same time.

If you fit this adjustment screw in place of the special one you can also do away with the two way valve and not involve the no82 relay/control unit as well.

This is the two way valve on the bulkhead.

The pipe labeled A is a vacuum pipe from the back of the carb, pipe B is the pipe to the bypass idle screw and C is the electrical connector from no82 relay/control unit.

You will need to take off and block pipe A coming from the carb (leaving it on at the carb end) , pipe B will be lost when the special bypass idle screw is removed and connector C can be unplugged.

This is showing the special bypass idle speed control screw arrowed blue with a metal shield/cover surrounding it.

The pipe labeled B is from the two way valve.

Same picture but with the cover removed.

Here you have the fancy bypass idle screw fitted as standard on the top and on the bottom a much simpler version from the 1B1 carb from the Nova.

Here is the bypass idle screw from the 1B1 carb off the Nova fitted , arrowed blue.

This should be adjusted to give an idle speed of about 850 rpm.

The screw arrowed red sets the basic throttle position by changing the resting position of the throttle plate , and hence the basic idle speed, which should be around 550 rpm when the bypass idle screw arrowed blue is screwed in fully. But you would only need to adjust this if it has been disturbed.

If you need to adjust the idle mixture this picture shows the idle mixture adjustment screw arrowed green. Screwing it in weakens the idle mixture , out enriches it.

(Also the part labeled A is the part load enrichment valve and the part labeled B is the idle cut off solenoid )

Generally without a gas analyser you set the idle speed to around 850 rpm with the bypass idle screw and screw the mixture screw in till the revs start to drop and then back it off about one quarter to half a turn.You will probably have to unscrew the idle mixture screw a bit to start off with, so when you screw it back in you can judge properly when the revs start to drop.

I have a cheap Gunson gas analyser and the settings above gives about 1.5% - 2% CO.

I did this idle screw modification at the same time as fitting the manual choke some years ago and it made things a lot simpler.

Edited 6 March, 201016 yr by William24

why cant I view the pictures? This would be very useful to me as I think my '89 polo cl is suffering with both of these symptoms

Edited 27 February, 201016 yr by brightsideteeem

can someone send me the pictures so i can view them??

I wrote that article and I can't see the images anymore either. I have contacted admin but have had no joy so far.

The images are hosted on the Club Polo site itself so I don't know what has happened.

I have Pm'd you as I have them still on the PC.

Images are now on Photobucket and are visible again.

Edited 9 March, 201016 yr by William24

You are a God, than you very much!