You have what sounds like a classic case of "leak off pipe failure".

These are the cloth covered pipes that connect between the injectors and carry the un-injected fuel back to the tank.

When they age they get brittle and can let air in. This means on each cold start where the car has been stood you are effectively re-bleeding the fuel system each time.

A small amount of air gets in and this allows the fuel to drain back to the tank.

You can get a length of fuel hose very cheaply to sort this. Getting the old ones off is easiest using a stanley knife and cutting them.

Let us know how you get on.