Fuel system upgrades for the MGA fall into three loose groups: items that address the age-related deterioration of original components in service (flexible hose, filters), items that support a modified or tuned engine (higher-flow air filters, uprated fuel pumps with matched pressure regulators), and items that add safety or convenience functions the factory system did not include (inertia cut-off kits). Because the MGA has been on the road for over sixty years and is now almost universally run on modern pump fuel rather than the leaded petrol it was built for, some of these "upgrade" items are now effectively service items for any MGA in regular use. Others remain genuinely specialist, appropriate to tuned engines or competition preparation rather than to a standard road car.
Why upgrades exist
The original MGA fuel system was designed around the fuel grades available in Britain between 1955 and 1962 and around the output of an unmodified B-series or Twin Cam engine. Modern pump fuel is ethanol-blended, which attacks unblended natural rubber hose of the original specification. Tuned engines running a Stage II or higher-tune cylinder head draw more air and more fuel than the standard system was set up to deliver. And modern expectations of safety in a classic car include features, such as automatic fuel shut-off in the event of a collision, that were not part of the original specification.
Upgrade parts address these points either singly or in combination.
Performance air filters
Performance air filters replace or supplement the original Vokes pancake (pushrod) or elongated oval (Twin Cam) air cleaner, giving reduced intake restriction and in most cases a serviceable element rather than the original oil-wetted mesh. On a standard engine the benefit is a modest improvement in throttle response; on a tuned engine with a Stage II cylinder head and matched camshaft, a lower-restriction filter helps ensure the carburettors can deliver the airflow the engine is now capable of. Filter kits are supplied matched to the carburettor type, H.4 for pushrod cars, HD.6 for the Twin Cam, and the correct variant should be specified at ordering.
Performance fuel pumps
Performance fuel pumps deliver a higher flow rate than the standard SU HP-type (pushrod) or LCS-type (Twin Cam) pumps. They are appropriate for engines built significantly beyond standard specification, where the original pump's rated delivery would become the limiting factor at sustained high RPM, and also for cars whose original pump has reached the end of its service life and where the owner prefers a modern solid-state replacement rather than a points-pattern rebuild. Crucially, a higher-flow pump should be ordered alongside a fuel pressure regulator (see below): higher delivery pressure directly to an unregulated SU carburettor will overwhelm the float needle valves and cause flooding.
Fuel pressure regulators
An adjustable fuel pressure regulator is fitted between the pump outlet and the carburettor feed on cars running an uprated pump. It allows the delivery pressure reaching the carburettors to be set to the 2.5 to 3.0 psi range that the SU float chamber valves are designed for, regardless of the pump's actual output. A regulator is not required on a standard SU pump feeding standard SU carburettors, the original pump is already pressure-matched to the float chambers. Ordering a pump and regulator as a pair is the normal pattern for any fuel-system uprating.
Stainless braided fuel hose
Stainless braided fuel hose replaces the short flexible sections of the standard fuel line with a heat-resistant, ethanol-compatible alternative. The braided outer sheath protects the inner hose from abrasion and under-bonnet heat radiation, and the inner liner is specified for modern pump fuel. Braided hose is often selected as much for appearance as for performance, it sits well in a restored engine bay, but its practical contribution is to durability, particularly on cars running modern ethanol-blended fuel where original-pattern rubber hose deteriorates within a few seasons.
Fuel cut-off kits
A fuel cut-off kit incorporates an inertia-activated valve that automatically interrupts fuel supply in the event of sudden impact. On an MGA the electric SU fuel pump runs continuously whenever the ignition is on, so a ruptured fuel line after a collision would otherwise continue to be fed until the ignition was switched off. An inertia cut-off provides a critical safety improvement not part of the original specification and is a sensible addition to any MGA in regular road use.
Ordering considerations
When ordering air filter and fuel pump upgrades, the engine and carburettor type must be specified, H.4 pushrod or HD.6 Twin Cam.