Fuel lines to carburetor draining completely

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I'm trying to get a 72 240z running and have noticed that it's fuel lines leading from the mechanical fuel pump to the carburetors are draining within 1-2 minutes. It has dual carbs with clear lines running to each carburetor so fuel in lines (and lack of fuel) is clearly visible. Is this normal, or should I be looking for a leak in the lines?

[shtu]

More likely a fault in the fuel pump.

Switch off, pull the feed from the tank off the pump, there shouldn't be fuel draining back through.

Depending on the specifics of the pump, might be a diaphragm, might be some sort of check valve.

[Decky_Q]

I have restored a few classics with mechanical fuel pumps and this is pretty normal, there will be fuel in the float bowl for starting and them pump will supply a flow before that is used up. An electric pump replacement gives a totally different starting sound.

Have you checked the diaphragm in the pump to make 100% sure it isnt perforated? If you check that and it's good then I wouldn't worry about it.

Are your clear fuel lines e10 safe? I have changed a few cars and boats lately to deal with the new fuel, and found the nicer looking lines to be non complaint, so black industrial looking lines had to be fitted in place of clear and coloured lines.

[Peanut Gallery]

As above, return valve in the fuel pump is what I would look at.

Old car, every time I turned the car off, the latent heat would heat soak the fuel, increase the pressure in the pump, and push the non-return valve out, draining everything back to the tank. Drove me mad.

[PaulKemp]

You could fit a non return valve further back in the line to keep more fuel in the line for startup