Cornwall Austin Seven Club creating interest in Austin Sevens (1922 - 1939)

I had a Zenith 26VA carburettor that was in very good condition apart from some wear on the throttle shaft. The two choices I then faced were either a) leave as it was and see how it ran and idled, or b) attempt some kind of overhaul.

Burden Fuel Systems supply a service kit for the 26VA. Burlen also overhaul customer carburettors, which is especially useful if the carburettor body is worn as the reaming required needs to be precise.

The service kit arrived complete with a new spindle and butterfly plus gaskets and seals etc. I then carefully stripped the worn spindle assembly by removing the arms that operate the choke and the throttle (The carburettor was on a workbench NOT in the car!). The screws that hold in the butterfly are very tight because you don’t want them falling out into the inlet tract, so select a good fitting screwdriver. The wear on the shaft then became apparent as can be seen from the photo. This was good news because the body was not particularly worn meaning expensive reaming would be unnecessary. Of course to do the job properly you would probably have the body reamed and then a new shaft fitted to suit, but this is unnecessary if your body is not too bad, and our little cars are supposed to be cheap to look after so unnecessary expense is best avoided if at all possible.

A trial fitting confirmed that the new spindle fitted nicely in the body without any real play and no tight spots that would indicate the shaft holes in the body were out of round.

NOW FOR AN IMPORTANT NOTE ON REASSEMBLY The butterfly has a bevelled edge meaning it can be fitted rightly and wrongly!

The picture should explain what I mean.

Correct orientation is important because else you will have difficulty getting the idle settings right due to the butterfly not closing off the inlet tract correctly. N.B the butterfly sits right near the air bypass port (the two small holes that can be seen just by the butterfly) this is fed via the jet that can be cleaned by removing the small brass screw found underneath the carburettor about 30mm back form the flange. Reference to cleaning this jet can be found in the technical section of the club website.

The two securing screws can now be fitted and done up tightly with a well fitting screwdriver, and the throttle and choke levers refitted in the same orientation as before. All that remains is to start up and re adjust your idle settings and hopefully benefit from a nicely idling engine.

The heavily worn old spindle

The brass cover removed to expose
the bypass drilling/jet

This article, written by Steve Martin, originally appeared in CA7C Seven Focus in Jun 2005 pp21-22.

Cornwall Austin Seven Club creating interest in Austin Sevens (1922 - 1939)

Last updated: 04 February 2012

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Carburettor Throttle Spindles

Last updated:
04 February 2012