I dont have the real answer for you but i have an alternative... It would seem that something is a bit sticky, i might suggest that maybe the flap doesnt move as you crank it, so its not opening any valves and giving you fuel, and poking it relieves any stickyness from being left over night, making it deliver fuel and start ok, and continue to run. If this is whats going on, you could either set about disassembling for a deep clean, or you could setup a cleverly positioned pipe with a long flexible something or other pushed up it, so you can use this as your pokey finger while still inside the car. This would double as your security mechanism for not being able to start it. I might expect this fault to get worse with time though, if it is indeed sticky. I hope it helps.