The fuel system is where the differences between the standard TD, TD Mark II, and TF are most pronounced. The three specifications use different carburettors, air filtration, inlet manifolds, and, on the later TF, fuel pump arrangement. The TF itself has a further pump change creating another parts split, so identifying the carburettor type and fuel delivery system is essential before ordering.
Carburettor Specifications
The standard TD used twin SU H2 carburettors of 1¼-inch bore. The TD Mark II was upgraded to twin SU H4 carburettors of 1½-inch bore. The TF retained the H4 bore size but used a different specification. These three carburettor types, H2 for standard TD, H4 for Mark II, and a different H4 for TF, determine which rebuild kits, gasket sets, service kits, dampers, spindles, discs, float chambers, and numerous other components are correct.
Piston springs differ by model: light blue for the standard TD and TF, red for the Mark II. Dashpot screw quantity differs, four for the TD, six for Mark II and TF. Plastic-cap dampers are standard, with brass-cap upgrades available across all three. On the TF, dampers were added to the dashpots from chassis TF/3495 in February 1954.
Carburettor Needles and Tuning
The needle profile controls fuel mixture across the operating range. The TD uses the ES (AP weaker, EM richer); the Mark II uses LS1 (AQ richer); the TF uses GJ (GL weaker, H1 richer). Needles are not interchangeable between H2 and H4 carburettors, the profile is matched to bore diameter and jet size. An SU tuning tool kit with jet adjusting spanner is available for carburettor setup.
Fuel Delivery, TD and Early TF
The standard TD used a single SU electric fuel pump on the right-hand bulkhead. The TD Mark II used twin pumps to meet competition fuel demand, a primary pump fed from the tank, and a secondary pump with its own pipe, adaptor, and hose feeding the front carburettor.
The early TF up to chassis 1509 retained the TD's low-pressure bulkhead-mounted layout.
Fuel Delivery, TF from Chassis 1510
From TF chassis 1501 in December 1953, the high-pressure SU pump replaced the low-pressure unit, with the parts supersession occurring at chassis 1509/1510. The pump was relocated from the bulkhead to the right-hand chassis side member ahead of the rear wheel, changing fuel pipe routing, mounting kit, and inter-carburettor hose specification. A rubber cover protects the chassis-mounted pump from road spray. At XPAG/TF engine 312, the filler plug was modified to make the pump self-priming.
Fuel Tank
The fuel tank is a 12½-gallon unit strapped to the rear of the chassis and painted to body colour. The TD and TF use different tanks with model-specific support brackets, but share common internal hardware (sender unit, filler cap, drain plug). Chrome end panels are available for show-quality restorations.
Air Filtration
Air filtration is one of the clearest differences between the three specifications. The standard TD uses a single filter assembly above the carburettors, feeding both through a shared air manifold. The Mark II uses the same layout with H4-specification gaskets. The TF uses individual oil-bath assemblies, one per carburettor, mounted directly to the carburettor bodies for enhanced dust filtration, with replaceable elements, felt pads, and a breather pipe to crankcase ventilation.
Inlet Manifold
The inlet manifold exists in two bore sizes: 1¼-inch for the standard TD (H2), and 1½-inch for the Mark II and TF (H4). Manifold-to-head gaskets, studs, clamps, and nuts are common. The carburettor-to-manifold spacer differs, the TD uses one specification; the Mark II and TF share a different spacer, with the TF needing more gaskets.
Performance Air Filtration
For improved airflow, chrome pancake filters, SU-style chrome filters, and K&N high-flow filters are available in both 1¼-inch and 1½-inch sizes to match the carburettor. Stub stacks pair with K&N or SU pancakes for further improvement. Performance filtration may require richer needles to compensate for reduced airflow restriction.
Ordering Considerations
The carburettor specification (standard TD, Mark II, or TF) is the essential reference for rebuild kits, gasket sets, service components, dampers, springs, and needles. For fuel pumps the chassis number determines whether the TF uses early low-pressure or late high-pressure specification, and the Mark II requires twin pumps with their own fuel-line set. Tank, pipe routing, and pipe sets are model-specific. Always identify both carburettor type and chassis number before ordering.