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Fuel pump controversy....

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JedFurneaux
Posts: 96
Joined: Tue Jul 11, 2017 5:50 pm
Location: Tregoss Cornwall

Fuel pump controversy....

Post by JedFurneaux »

Advice please!
My 1934 Daimler LQ2/20 is retro fitted with two SU electric fuel pumps (one 'main' and one 'reserve'). I hate the bloody things as they are forever 'sticking'. The previous owner (who inherited them with the car) suggested that these cars are prone to fuel vaporisation when hot and that the electric pumps helped cure this. I didn't feel inclined to take issue with him but I fail to see how this could be so. I am sure that the original mechanical pump supplied adequate pressure and the flow between the pump and the carb is controlled by the float and needle valve in any case. On the car the original pump (sadly bereft of it's operating lever), reserve switch and original pipework are all still in place and I would like to re use them and get rid of those bloody awful electric things but I would seek the advice of those who have more experience with these engines before I start ripping them out.

1) Is there any disadvantage in reverting back to the mechanical pump?
2) Where can I find the appropriate operating lever?
3) If indeed 'fuel vaporisation' is an issue with these engines then can it be cured by fitting a heat resisting washer between carb & manifold like the set up on my old Norton 650SS motorcycle?

Thanks, Jeremy.

qantasqf1
Posts: 299
Joined: Mon Mar 07, 2016 10:13 pm

Re: Fuel pump controversy....

Post by qantasqf1 »

Jeremy, you’re quite right in your reasoning about fuel vaporisation - fuel will vapourise in the lines irrespective of whether you have a SU electric pump or an AC mechanical pump. The primary advantage of the electric pump is that it’ll prime the carburettor when you switch on the ignition so you don’t have to open the bonnet and mechanically prime it with the AC pump’s external lever. In addition SU electric pumps are pretty reliable beasts and if yours keep sticking then almost certainly a new set of points and a new diaphragm would sort them out. I agree it’s a shame your AC pump’s lever is missing because in the interest of ‘Daimler purity’ (!) I personally would prefer to use the original pump, but unless you have a pattern it maybe difficult to find the correct one as they vary from one engine type to another. Fitting a heat shield between the carburettor and the inlet manifold works up to a point, but that’s not totally successful - I can speak from personal experience here in Australia! In short, why not overhaul your SU pumps?
Cheers
Steve

JedFurneaux
Posts: 96
Joined: Tue Jul 11, 2017 5:50 pm
Location: Tregoss Cornwall

Re: Fuel pump controversy....

Post by JedFurneaux »

Thank you for your reply and counsel, Steve. I will try and find the correct lever.
I don't know where in Australia you live but I was fortunate to have many wonderful times in Melbourne/Victoria and Tasmania for a few years.
Very best wishes,
Jeremy.

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