How To

Since 1961, VWs are equipped with an automatic choke. A bad adjustment can have important consequences on the mileage and the overall efficiency of the engine. So, the fine tuning of this accessory is not as insignificant as it looks like.

At first, let’s look at the location of the automatic choke. The system is constituted by a "case" inserted in the body of the carburetor. Inside you'll find a plastic cap and most of all an active element called " choke heating element ". It is situated on the right side of the original Solex carburetors. The automatic choke is electrically fed as soon as the contact is turned on.

The way the Solex automatic choke works is simple. Before starting the car, the driver steps on the gas. This will engage two actions:

· The choke butterfly is released and a spring situated in the mechanism of the choke is keeping it in the closed position

· When closed, the choke butterfly axle is connected to the idle cam which is going to maintain the throttle butterfly in accelerated position

Less air, more gasoline, this is the cocktail of an "enriched" mixture which helps the engine to start under cold conditions.

The return to the normal position (this means stopping the choke) is managed by the expansion of the spring which is going to return the choke butterfly in its normal position, thanks to an electric heating element.

How is the automatic choke assembled? Many breakdowns of the choke are resulting from a bad assembly. The most frequent is due to the spring which does not catch the control lever which is opening the choke butterfly.

On the below picture, solex 28 pict 1 :

upper right : the choke mechanism with the electric connection

upper left : The choke is on, the idle cam is maintaining an fast idle

Bottom : The choke is off, the idle cam is in its normal position, the idle is normal.

What we just saw was purely mechanic, but what is going to be very interesting is to see in what conditions the choke system is going to close the choke butterfly, speed the idle and when (and in how many times) it is going to be automatically stopped.

This automation is controlled by the “choke heating element”, the position of the spring depends on its temperature, this temperature is obtained with an electric flux passing through a heating element which is inserted into the spring.

When cold, it is positioned to close the choke butterfly and accelerate the idle. When hot it is releasing the pressure on the choke butterfly.

That's why the good condition and adjustment of this “choke heating element” is going to have an influence on the whole choke system.

Like I said before, the lever of the throttle butterfly needs to be positioned into the spring hook, but the choke heating element needs to be positioned properly in the carburetor also. Because everything is depending on the heating element spring tension, difference in its function will depend on its position.

That's why you'll find some marks on the carb and on the choke heating element. The factory adjustment is to place the marks in front of each other.

To adjust the efficiency of the choke you just need to turn the choke heating element in the carburetor. Depending on the quality of the choke heating element but also of how you are driving your car or even the different engine adjustments. The choke adjustments can be slightly different from the factory specs.

From the factory marks, if you are turning the choke heating element clockwise you are going to diminish the choke effect, the choke butterfly will be less closed. The air/gas mixture will be poorer, the idle will be less accelerated, and the return to a normal position will be faster.

If you are turning the choke heating element counter clockwise, you will have the reverse effect. When the butterfly is closed more, the mixture will be richer, the idle more accelerated and the return to a normal position longer.

Those adjustments need to be made when the engine is cold.

We just saw different troubleshooting or malfunction of the starter: The spring not attached to the choke butterfly lever and the choke heating element malfunctioning. Also, if the choke butterfly is not coming back correctly in its normal position, the idle adjustment is going to be impossible to do and the air/gas mixture is going to be too rich, meaning poor gas mileage and bad efficiency of the engine.

Another breakdown can simply come from an electrical problem. If the heating element is not warming up correctly, the spring will not lose its tension. Usually it is because the electric flux is bad, check the wiring and fuse, or the heating element may be burned ( if you changed your car from 6V to 12V for example), and you'll need to replace the choke heating element.

Have fun now !!!

Seb