Imagine finding an A or 4A Roadster ready to restore. As you delve into the minutiae of its various parts you discover that the throttle cable is in the box ‘o bits that came with the car. No problem! A cable in a sleeve, hook it up to the pedal and voila. Problem is thought, that the pedal does not pull on the cable, and nothing in the floorboards or anything else can give you a clue on how it works… or does it?
EXHIBIT “A” the throttle cable: Simple enough, a cable inside a larger cover. The inner cable is longer than its cover. No problems so far.
EXHIBIT “B” the toe-board: Above the hole for the pedal we see a small hole. Interestingly enough that hole lines up directly with the hole in the pedal. There is a bracket on the toe-board above the hole. That bracket holds a wire the same diameter as the inner throttle cable.
EXHIBIT “C” the throttle pedal: Spring loaded to return to the “off” position, the throttle pedal also has a small tube welded on the pedal arm in line with the movement of the pedal. This tube has different diameter openings at the back vs the front. The back opening is larger, the same diameter as the outer throttle cable cover, the front opening is the same as the inner throttle cable. Hmmm.
EXHIBIT “D” The clamp on the valve cover: This clamp is designed to secure the outer throttle cable cover, yet it is bolted to the valve cover and not the carburettor.
How everything goes together:
This is definitely a situation where one must think “outside the box”. First we will install the inner throttle cable. The “toe-board” end is passed through the tube on the throttle pedal and through the hole in the toe-board. Once through, it is secured from the inside of the passenger compartment. The throttle pedal MUST be able to move freely and the cable should not interfere or bind as the pedal moves back and forth.
Now we can slide the outer throttle cable cover over the inner throttle cable. The “pedal” end of the tube will fit in the larger (front) end of the tube. The combined cable is then clipped to the inner wing (right – or driver’s side) by the way of a clip through one of the bolts for the bonnet clamp. The “carburettor” end of the cable is secured in the bracket on the valve cover.
With the “carburettor” end throttle cable secured, the inner cable can now be attached to the arm of the butterfly valve of the carburettor.
How it works:
With this setup, the inner cable is not physically pulled by the throttle cable. In actuality, it is the outer cable that is affected directly by depressing the throttle. With the carburettor end of the outer cable secured, it is compressed by depressing the throttle pedal. This action has the effect of pulling the inner cable though the outer one and in turn pulls the butterfly valve open.
(click on the graphic below for a closer look)
Who would have guessed?