Earlier models were fitted with the PD type of pump shown in Fig. 30 Later models have the type of pump illustrated in Fig. 31, which is basically similar to the other types of S.U. horizontal pumps with which many readers will probably be familiar. It does differ, however, in the arrangement of the valves and may have twin contact points. It is fully described on pages 76-8.
These later pumps are very reliable and seldom need attention which is, perhaps, just as well, as they are mounted beneath the car. The earlier PD pumps sometimes gave trouble and if a pump requires an overhaul there is a good deal to be said for replacing it by the later design.
This can sometimes give rise to a further trouble, however, as the later pump produces a higher fuel pressure, which may cause the carburettor
The earlier S.U. electrical fuel pump (type PD). The pump is mounted on the inside of the left-hand rear sub-frame side member:
1, contact-breaker cover; 2, filter cover
to flood. Rough idling, occasional stalling and difficulty when adjusting the carburettor will result and fuel consumption will suffer.
The cure is to replace the float-chamber lid with the later pattern which has a nylon-cased needle and a nylon float. If your car is one on which the fuel pump has been replaced by the later type but this modification has not been carried out, the new float-chamber lid can be fitted in a few minutes. The cost is about a guinea.
Still more recent engines (for example the Clubman and 1275 GT) have mechanical S.U. pumps, mounted on the bulkhead-side of the engine [see page 78).