::standfirst The SU fuel pump's reassuring "tick" means it's working; when it goes silent and the engine starves and stalls, the internal points have usually stuck. A gentle tap on the pump often frees them enough to get you home, but the real fix is cleaning or renewing the points, or fitting a good low-pressure replacement.
How it should behave
Switch the ignition on with the engine off and the pump should rattle away rapidly for a few seconds while it fills the float chambers. Once the needle valves close on full bowls, the ticking slows to the occasional single click as the pump tops up against the closed valves. On the road, you should barely notice it, a soft, intermittent tick under load, near-silence at rest.
Rapid ticking on priming, then near-silence: that is a healthy SU pump.
The classic failure, it goes silent
The engine stumbles, coughs, and dies. You turn the ignition off and back on and there is no reassuring rattle, just silence. The points inside the pump have stuck closed or dirtied, and the coil no longer pulls the diaphragm.
The traditional roadside fix is a firm but gentle tap on the pump body, the handle of a screwdriver is about right, not a hammer blow. The jolt is usually enough to unstick the points, the pump starts ticking again, and you can drive home. Treat it as a get-you-home measure, not a repair: a pump that has stuck once will stick again, and the next time may be somewhere less convenient.
Roadside checklist
SU fuel pump, quick diagnosis
Step 1 of 5
1.Ignition on. Is the pump silent, no reassuring tick, tick, tick?
The other complaint, it never stops ticking
The opposite fault is a pump that ticks on and on at idle and never settles. That means fuel or pressure is bleeding away somewhere and the pump keeps topping up to compensate. Work through the likely leaks in order:
- Float-bowl gaskets. A weeping gasket between the float-bowl lid and body will let fuel seep out and drop the level; the pump refills endlessly.
- Fuel line and unions. Perished rubber hose, porous flexible sections, or a loose union between the pump and carbs will lose pressure between ticks.
- Needle valves not seating. A worn or dirty needle valve lets fuel through even with the float up, flooding the bowl and running fuel out of the overflow.
- The points themselves. Worn or dirty contacts can stop the pump latching properly at the end of a stroke, so it cycles continuously instead of resting.
Check gaskets and lines first, they are cheap and visible, then work back to the pump.
Proper repair and replacement
Once you are home, do the job properly rather than trusting the next tap.
Clean and adjust the points. Remove the bakelite end cover, ease the points apart, and clean the contact faces with a strip of fine abrasive paper or a points file. Clean the pedestal underneath and check the throw of the rocker. Set the contact gap to the figure in the workshop manual for your pump.
Renew perished fuel line. Old rubber hose degrades from the inside out on modern ethanol-blended petrol. Replace any suspect sections with modern ethanol-resistant hose rated for continuous fuel service, and use fresh clips.
Choose a correct low-pressure pump. The SUs on a T-Type want around 2.5–3.5 psi. Your realistic options are:
- an original-type SU pump, rebuilt with fresh points and diaphragm;
- a good reproduction SU with modern solid-state or standard points;
- a low-pressure Facet-type electric pump rated in the same 2.5–3.5 psi range.
Positive-earth note
These are positive-earth cars. Wire the pump accordingly, the switched feed goes to the pump's live terminal and the pump body earths through its mounting to chassis positive. Reversing the polarity on a solid-state SU replacement will destroy the electronics on first switch-on.
Related reading
- Roadside diagnosis of a silent SU pump, the quick checks to make before you take the pump off.
- Setting up the twin SUs, once fuel delivery is sorted, the carbs come next.
- Cooling the XPAG and XPEG, the other classic "it stopped by the side of the road" story.
FAQ
Why does my SU fuel pump keep ticking? Continuous ticking means fuel or pressure is leaking away between strokes. Check float-bowl gaskets, fuel lines and unions, and the needle valves before blaming the pump itself.
My MG won't start and the fuel pump is silent, what do I do? Tap the pump body firmly but gently with a screwdriver handle. If it starts ticking, the points had stuck; drive home and clean or renew them properly. If tapping does nothing, check the pump has power and a good earth before condemning it.
What pressure should an SU fuel pump run at? The SUs on a T-Type are designed for roughly 2.5–3.5 psi. Higher pressures overwhelm the needle valves and flood the carbs.
Can I fit a modern fuel pump to a T-Type? Yes, provided it is a low-pressure type in the 2.5–3.5 psi range, a low-pressure Facet-type is a common choice. Avoid high-pressure pumps intended for fuel injection, and be sceptical of pressure regulators sold to reduce them.