Fuel being forced through carb

[niwid]

We’ve got a bit of mojo back and found some time to spend on the Acty, so we’ve been addressing the fuelling issue that stopped it getting to RRG this year. The tank was disgusting, so we cleaned it out with oven cleaner which worked a treat. We then discovered that the original fuel pump was junk, so bought a facet electronic pump and fitted that in it’s place. Plumbed it in, turned the key and hey ho it’s pumping fuel. However, it doesn’t stop pumping, and fuel is leaking through the carb into the air box (engine not running). Fitted a pressure regulator to restrict the flow, and still it’s happening (even when turned right down to 1psi). We took the carb apart and cleaned out the float chamber and fuel inlet in case there was crud stopping the needle valve from closing properly, we also tested the needle by blowing through the fuel inlet and it seems to work fine. I’m wondering if there should be a switch or something that turns the fuel pump off when it reaches a certain pressure, but I was under the impression that was already taken care of by the pump and pressure regulator? What am I missing?

Thanks in advance

[Dez]

does it have a return line to the tank? really cars with electric pumps should have, so it gives the fuel somewhere to go when the float valve is shut, rather than trying to pressurize a dead-end.

[niwid]

No, it had an electric fuel pump as standard though with no return. I had thought about this, but assumed it would be fine as it came like it from the factory. Is there a way of easily adding a return?

[Dez]

not really! I'm not a fan of cars without them though- I'm my head theres very few cars that don't need one. sending the fuel back to were it came from has always got to be better than shutting it off and it causing unnecessary pressure/strain on the pump, lines and carb float valve. depending on what your tank is like you can often put them back in through the sender unit so you don't have to mod the tank, but it still means running an extra line full-length of the car and modding/swapping the carb unions/lid.

saying that, it may no necessarily explain your problem...

[niwid]

Yeah I've always thought a no return setup would put strain on the pump. The carb is only about 2ft from the engine (rear mid mounted engine and mid mounted tank on a 3.2m long vehicle) and the tank just has a 6mm pick up pipe coming out of the top and into the fuel pump above it so running an extra line isn't a problem. I used to run a T piece on my old Polo, with one end coming from the pump, another going to the carb and the other going to return which replaced the damaged swirl pot. The carb only had an inlet, no return, and it would just take what fuel it needed and the rest would go back to the tank. But then on the Acty, there is still no return to tank so unless there is an easy way to fit one it's still a no go and as you say still may not explain the leak.

[MrSpeedy]

If it's an electronic pump then it'll automatically shut off when pressure is reached anyway. - No problem.
If it doesn't switch off then I'd question it's origins.

If the carb is still leaking fuel at just 1psi I'd be more inclined to think it's a float chamber issue. Either the level is too high or the needle valve is leaking.

My Trump runs Strombergs (notoriously leaky) with an electronic pump (a modern electronic version of the old SU pump) and with the fuel pressure regulator set at 2.5psi there has been no leaks for the past 3 years