Fuel return valve series 3 V12

[vee12eman]

Hi,

In response to a couple of fuel leaks I have replaced the fuel flexible lines in the engine bay, taking the opportunity to renew the fuel return valve at the same time. Previously, the pump ran prior to starting, then either slowed down or even stopped. Now, it continues to run and I can hear the fuel return valve “fizzing”, which seems to indicate it is doing it’s job. However, I never heard this before and yes I have checked for leaks etc. under the same operating conditions so, as this is different to previous experience, I am just checking that this is normally the case.

The system is otherwise standard with Strombergs and being a very early UK car (built in January 1971) there’s no emission gear except the very basic original design. Other modifications are to ignition and cooling system which will not affect the fuel.

Regards,

Simon

[lowact]

Should do what it did. Have you put it in backwards?

[Bob.]

Hi Simon,
My view is that the system you have now is normal for an S3. The "before" scenario is typical of a non recirculating system as fitted to the S1/S2 cars but the system in S3 is designed to recirculate fuel continuously to keep it cool enough to avoid vapour locks as underbonnet temperatures are higher than for S1/S2. The pump should settle down to a regular ticking once the float bowls are filled. The pressure relief valve should sizzle continuously as it is there to maintain a pressure at the carbs of 1.5psi whereas the pump produces about double that.
Bob

[jagwit]

...the system in S3 is designed to recirculate fuel continuously to keep it cool enough to avoid vapour locks as underbonnet temperatures are higher than for S1/S2. The pump should settle down to a regular ticking once the float bowls are filled. The pressure relief valve should sizzle continuously as it is there to maintain a pressure at the carbs of 1.5psi whereas the pump produces about double that.

Absolutely correct Bob!!

Its worth adding that the non-return valve should "sizzle/buzz" also to allow purging of fuel vapour in the fuel rails if the hot engine was switched off allowing heat soaking to boil the fuel (now in gas form) in the fuel rails, replacing it with cooler liquid fuel.

Before I sorted the cooling system issues on my car (which turned out to a non-sensical otterswitch), I could HEAR bubbles flowing through the fuel pipes after switching on ignition, but before cranking with a heat soaked start.

[vee12eman]

Thanks for all the replies. I was fairly certain I now had a correctly operating system, but after so long of not being this way, I was suspicious. I re-used the original ball return valve when I rebuilt the car, it was in the right orientation so perhaps someone had replaced the spring with a stronger one at some point.

Regards,

Simon

[jagwit]

I once had issues on a classic Range Rover and it turned out to be the return line from the engine to the tank that was blocked.

For the sake of others reading this thread, I thought it worth while mentioning that the return line should also be open to allow flow of fuel.

[Bob.]

When I first had my S3 and was trying to solve rich running problems, amongst other issues I found the return pipe blocked inside the fuel tank. It was adjacent to silver soldering between the take off and return pipes, done presumably to stiffen the assembly. Probably caused years ago by internal corrosion where the heat from the soldering had damaged the internal plating of the pipe, followed by a long period of storage with the tank part full.

[lowact]

The valve in backwards may not stop the flow completely and doesn't need to, I can blow through mine backwards is I try really hard.
I once had a badly blocked fuel filter when driving overnight, Melb to Canberra. Didn't realise at the time that that was the problem. Couldn't overtake a skateboard. Best mileage I've ever achieved. Interestingly the "non return valve" was sizzling so loudly I could hear it from the cabin.