Originally Posted by MarkN

Both the XR3i and RS1600i have overrun cut off. This is essential in the K Jetronic system because it allows the plunger in the metering head to drop back when you are decellerating.

The overrun valve is opened when the engine is at normal operating temperature, the throttle is fully closed and the revs are above 1500 (I think) rpm and dropping.

The two cars implement it into two different ways. The RS1600i's ECU controls the valve. When it detects all of the above conditions it opens the valve and allows the plunger to drop. When this happens BOTH the red and amber lights illuminate on the speedometer. They do not work seperately.

The XR3i has no ECU, so instead it has a speed-sensing relay behind the dash that monitors the tacho signal and when the conditions are right this opens the valve. It doesn't have the lights on the dash so it is not obvious that this is happening.

When someone converts an RS1600i to run on a distributor they tend to forget that without the ECU working the overrun valve won't function. This being the case the car will hestitate and kangeroo on overrun. It would be possible to fit the XR3i speed sensing relay to solve this but for some reason people don't seem to do it.

You can check that the overrun system is working correctly by getting the engine up to operating temperature, and opening the throttle slightly from under the bonnet. When you release it you should hear a "click" from the valve on the back of the fuel distributor. If you don't then the system isn't working. The cause of this is nearly always the contact on the throttle.

The econolights on carb fed Fiestas, Escorts and Cortinas are all operated via two vacuum switches. On these cars the two lights do work separetely, but on the RS1600i they always work together.