Thread: Petrol Pump

Gentlemen,
I have always understood that on carburettored vehicles, the petrol pump should be as close to the tank as possible and preferably mounted slightly below it, with any pressure regulator being as close as possible to the carburettor.

I understand that this arrangement is designed to ensure that the fuel in the fuel line does not drain back into the tank, forcing the pump to have to suck fuel from the tank during cranking, as electric pumps are designed to push, rather than pull. Also, if the fuel line between the tank and the pump is empty and long, then there will be no fuel l flowing through the pump to cool it, resulting in much greater wear and tear on the pump.

However, on our vehicles, have been designed to have the petrol pump mounted as high as possible on the firewall, way higher than the tank and with quite lengthy fuel lines able to drain back into the tank overnight.

Has anyone tried to mount the fuel pump closer to the tank or even level with the tank?

I'm interested in the views on this subject, of our resident experts. It just seems counterintuitive to me.

regards and thanks in advance,

Jeff

Originally Posted by 1950landy

The pumps used in series LR's are low pressure pumps & they have good suction but not a lot of pressure to the carby , where pumps mounted near the tank are the opposite, The valves in the pump will prevent drain back plus the glass sentiment holds enough fuel to prime the pump if needed & will supply the carby with fuel to start the engine .

Jeff,

1950Landy hit the nail on the head. The low pressure pump is correct for your 80". It has a light 1.5lb spring and a softer acting magnet coil, whereas the HP pump has a heavier 4lb spring and a stronger magnet. The LP coil housing normally has a 2BA earth terminal screw (approx 5mm) and the HP coil has a 4BA earth screw (about 3.5mm).
If you have the origonal pump on your 80, it may not have an earthing screw boss on the cast iron coil housing. The 80" models had a double ended earthind stud with a 2BA nut taking the place of the screw type earth on the later S1s. ( a bit of trivia). Check the 80" parts book if you need clarification. If the magnet coil housing is removed from the aluminium pump the raised central boss on the LP coil housing is about 15mm in dia. whereas the HP boss is about 18mm. Sometimes there is a part number stamped onto the brass coil retainer plate. if it ends in 6, it's a 6V if it ends in 7 it's an LP 12v coil. If the pump drains back or fails to prime, there is a faulty valve disc or air leak somewhere.
I rebuild a lot of them, so if you get stuck, PM me. They can be points or pos or neg earth electronic control, as required. Mike ,5380