24V fuel system

Technical questions and answers
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muz122
Posts: 4
Joined: Fri Sep 30, 2022 10:10 am

24V fuel system

Post by muz122 »

Hello all,
My first real post other than introduction a while back. I look after a customer's militiary 24V, which I've just completed multiple jobs on, including removal of the restrictors. It's running on a pair of Stromberg CD175's which I believe are factory? Here is the layout of the fuel system which I believe to be the cause of my issues:
Twin underseat tanks, sender in each tank.
1 x 24V electric fuel pump, unknown brand.
1 x changover valve in right footwell which mechanically controlls which tank the pump pumps fuel from and electrically switches the sender accordingly. The supply splits just before the left carb, therefore feeding both carbs.
Return goes back to both tanks constantly regardless of which tank is being used, which isn't ideal as the tank being used is only receiving half the return therefore depletes even faster than it should!

From my searches on this forum, it seems there should be a pump for each tank, controlled by the changover valve and the appropriate sender is selected via a separate switch. Or, should both pumps be constantly running (one pump per carb)? Also read somewhere here (can't find the thread now) that constant return fuel system should not have float valves? When I rebuild the carbs, they were fitted so I renewed them with the valves from the carb kit.

I would really like to return the system to standard but finding part numbers/wiring diagrams/system description is proving to be difficult. If anyone could shed any light or point me in the right direction, I'd be eternally grateful!

Many thanks,

Matt
map1275
Posts: 1076
Joined: Mon Jul 21, 2008 2:48 am
Location: Brisbane, Australia

Re: 24V fuel system

Post by map1275 »

I haven't had to do this for a while but basically, no.

If you look at your parts book the mechanical changeover switch is a double unit because of the fuel return. Other models are just a single. The pipework gets a little crazy with one pump. One fuel gauge, so the switch changes over sender unit feed at the same time.

I wanted twin tanks as a conversion so it took me long while to understand the differences of the V8 and presumably diesels vs the usual 2.25 and other military markets.

There are affordable electric, plastic changeover valves that are far more compact. In particular from not relying on olives and nuts to connect the hoses.

I'd also thought of fitting a second pump, more as a potential back up unit in addition to the changeover process.

The needle and seat has nothing to do with fuel return. Remove them and carbs will flood as fuel exits anywhere it can as the needle doesn't close the jet when the car is off.
muz122
Posts: 4
Joined: Fri Sep 30, 2022 10:10 am

Re: 24V fuel system

Post by muz122 »

map1275 wrote: Wed Dec 07, 2022 6:45 pm I haven't had to do this for a while but basically, no.

If you look at your parts book the mechanical changeover switch is a double unit because of the fuel return. Other models are just a single. The pipework gets a little crazy with one pump. One fuel gauge, so the switch changes over sender unit feed at the same time.

I wanted twin tanks as a conversion so it took me long while to understand the differences of the V8 and presumably diesels vs the usual 2.25 and other military markets.

There are affordable electric, plastic changeover valves that are far more compact. In particular from not relying on olives and nuts to connect the hoses.

I'd also thought of fitting a second pump, more as a potential back up unit in addition to the changeover process.

The needle and seat has nothing to do with fuel return. Remove them and carbs will flood as fuel exits anywhere it can as the needle doesn't close the jet when the car is off.

Thanks and Happy Christmas & New Year.
Just fitted a Facet 24V pump and an adjustable pressure regulator between pump and carbs, so far so good.
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