My car wont start/run on gas now after i ran out earlier today.

I presume i ran out anyway - the car should have been about empty  and
I was on my way to the petrol station when it suddenly lost all power.
I changed over to petrol and it started running again.

I then filled up with gas (though i only got 52l in a 70l tank), and
the car now wont start on or change over to gas when moving.

Is it possible to airlock the gas system or something by running it
empty? - or is it more likely that something else is playing up?

Generally when it is low on gas i notice it start hesitating and
stuttering a bit before it actually stops - but it just went suddenly
this time.

It did this once before and whatever it was seemed to solve itself
after it had been parked up for 48 hours and i'd metered all the
solenoids (which were all working).

Today the solenoids are all clicking as i'd expect.

However i get some wierd behavior (unless this is normal?)..

If I start the car on petrol and then switch it to nothing and let it
run till it stalls, then set it to gas and try starting it, it wont
catch.
If i then set it to no fuel again and try to start it, it will run for
about 10 seconds before dying. Is this usual?
Could it be a bit of petrol getting past the petrol stop solenoid as i
cycle through the choices of fuel even though the engine is not
running?, or could this be a bit of gas that is somehow getting
through?

The system is a simple open loop kit with a single mixer. I'm not sure
what type of switch it is (square, 1 button with 3 options and 5 leds
along the bottom)