Triple SU carburettors

The triple SU installation on the XK six is widely described as a perfect match to the engine, and the carburettors themselves are simple devices that are cheap to rebuild. An E-Type that runs roughly on SUs is more often badly set up than worn out, which makes the system friendlier to live with than its reputation suggests.

Ignition first, carburettors second

Mixture and balance adjustments assume the spark is arriving at the right moment. Retarded or wandering ignition timing will make the best-set carburettors run badly, and no amount of mixture work will cure it. The correct order is compression, ignition timing and points, then the carburettors. Anyone who reaches for the mixture nuts before checking the timing is working backwards.

Balancing three instruments

Each carburettor feeds two cylinders, and the three must draw the same amount of air at idle before the mixture is set. An airflow meter held to each mouth in turn gives the comparison, and the throttle linkages are adjusted until all three read alike. Only then are the mixture settings trimmed, one instrument at a time, listening for the fastest, smoothest idle. It is patient work rather than difficult work, and it transforms a car that has been adjusted by ear over the years.

Strombergs and Webers

US-specification cars from the late Series 1 and Series 2 ran twin Zenith Stromberg carburettors for emissions reasons. Converting a Stromberg car back to triple SUs is described as costly, and a Weber conversion can come out cheaper. Neither is original to a car that left the factory on Strombergs, which matters to buyers who care about originality and to sellers describing a car accurately.