[HI Cobra]

You haven't mentioned if it is firing when you prime it.
If it is then try adding 5 more gallens (put a bit of pressure
head from the tank) and continue to prime it.
I ran mine dry once and had to do this. It took several
attempts at priming before it pulled gas in. I have since
added an electric fuel pump in addition to the mechanical
that I have wired to a toggle and use it to bring the gas
pressure up prestart like in an airplane. It works great
for starting if it hasn't been run in a week. Once I am
going I shut the electric off.

Flip