Fuel Pump/Air

[fhwlloyd]

Normally when starting the car I switch on the ignition, wait for the fuel pump to stop ticking and then start. However when starting it the other day the fuel pump wouldn’t stop ticking. It was light on fuel so I topped it up thinking maybe that would help the pump. The engine starts and seems to run fine up to higher revs. However, there is a large amount of air trapped after the fuel filter which isn’t purging. How do I trouble shoot this? I can’t see/smell any fuel leak. I have a spare fuel pump but I don’t want to set about replacing unless necessary. It seems odd how it starts/runs ok but won’t purge this air and the fuel pump won’t stop prior starting.

Thank you in advance for any ideas/guidance.

1969 series 2 coupe.

[johnetype]

If your car has had it's original SU pump replaced by a newer SU pump with electronic 'points' rather than the original mechanical points the tick, tick, tick not stopping is normal behaviour.

If you still have the original style mechanical points pump then perhaps the accumulator on the pump isn't doing it's job properly.

I would expect any air to self purge after some spirited driving

[rdh6642]

On a mechanical SU pump, the ticking should stop a short while after switching the ignition on and before starting, when any air in the system has been vented at the float chambers, the float valves have closed and the system is pressurised. The electronic version differs in the means of actuating the pump but otherwise is identical in operation. Both types may tick occasionally with the ignition on as the pump valves slowly lose pressure but that might be twice a minute. Once the engine is started, fuel demand will drive the rate of ticking as the pump maintains steady pressure in the system under varying conditions of load. Simple and elegant but not without servicing needs.

Air trapped after the fuel filter and visible in the nylon line is very odd and suggests a lack of pressure in the system. If before starting the engine, the pump continues to tick and there is no leak apparent, you could loosen the connection between the nylon fuel line and the carb fuel pipe and see what happens.

When you mention the engine is running fine up to higher revs, do you mean while stationary or under load while driving?

[cactusman]

Check too there is not a tiny leak in the pipe leading from the tank to the pump. If there is the pump will pull air in as well as fuel from the tank....and the pump will tick endlessly.....happened to me a couple of times with my MGB which has an SU pump external to the tank

[christopher storey]

I have copied and pasted from the other fuel pump thread running at the moment

"I often wonder how many of these flooding problems are caused by misassembly of the float chamber securing nut and the slotted washer. It is odd that this is not referred to in the Burlen quotation, but if the slotted washer is not placed next to the lid (** I hope I've got that the right way round ) the chamber becomes airlocked and/or slightly pressurised which then causes fuel to rise in the jet

** Just checked and I have got it right"

This might conceivably account for your trapped air