Fuel enrichment

For a car to start from cold, you need a richer fuel-air mixture, modern cars use a computerised engine management system. Classic cars had a cable on the dashboard that pulled a lever on the carburettor(s) which allowed more fuel into the air stream. Guess which system is more reliable. Sometimes modern is not better.

Vintage cars are a bit light on engine management computers so a trusty cable system with a Bakelite knob mounted on the dashboard is in order. However, I really want to keep the instrument panel simple and elegant, a choke control is necessary but ugly. What else could I do instead?

Like a modern Grand-Prix car the Riley steering wheel has a bunch of control functions. Within a non-rotating central hub are controls for all the lights, the indicators, horn, distributor advance-retard and a hand throttle. All this is neatly wrapped in a Bakelite casting (unlike a modern Grand-Prix car). The existing hand throttle is connected via brass levers to the carburettor throttle linkage and is only used to increase the engine speed whilst it is cold. So that is part one of the enrichment solution inbuilt already.

The distributor advance-retard control is redundant because I have upgraded the ignition to modern distributor. So this gives me a control on the steering wheel that I could re-purpose. If you look at the picture below, the control in question is the metal item at 9 o’clock. The large teardrop ‘switch’ controls the indicators (non cancelling) and the control at 3 o’clock increments through side, dipped beam and full beam light selections. All of these controls connect to tubes inside the steering column and re-appear at the far end. You can just make out the hand throttle – its the black lever at 11 o’clock. That is actually mounted on the steering column just in front of the rev counter having been repositioned when I lowered the steering.

The challenge: the control on the steering wheel rotates (conceptually think left-right in an arc) but the fuel enrichment levers on the carburettors need to be pulled back, towards the driver. So how to convert a rotating left-right movement into a forward-backward movement. This took a fair amount of thought, because in addition I had to stay visually in period.

Below is a view of how the carburettor linkages are connected together and how they need to move – this is viewed from the side of the car


I then had a Eureka moment fuelled by (sorry for the pun) an understanding of how Etype Jaguar throttle linkages change the direction of motion a number of times. A quick sketch later and I had a conceptual solution.


If I inverted the rotating lever at the bottom of the steering wheel it would point outwards instead of inwards – so now when I move the steering lever the motion moves the relocated lever in an up down movement albeit in an arc. Converting an up-down movement  to a forward-back motion flipped at 90 degrees is easy if you understand lever principles and hopefully the drawing above explains it a little easier. There was a handy bolt on the steering box that just happens to be in a usable position. The ‘L’ shape lever needed to be fabricated from 2mm mild steel with the addition of a 20mm tubular spacer brazed on to the back to space the whole thing out from the steering box. All the parts were then connected together using spare throttle linkages and the result is this:


Oh I almost forgot, Part of the challenge was to get the linkages to miss the immovable engine mount!

I am jolly pleased with the results of this weeks challenge 🙂 Maybe I should have made everything from brass? No that is perhaps a step too far…



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