Seems that pressure wasn't enough I have the same back plate the hole is very small.
If I recall I was able to pass #30 gage motor winding wire through.

Things to check
Tank looking horizontally to the NV is level to or splitting above and bellow the NV.
Fuel line is true 1/2A size
Fuel line on the needle to avoid air leaks / loss of pressure
Prop to big not enough rpm for good crank case pressure.
All lines as short as possible
Fuel tank volume is too big at 2oz perhaps 1oz tank should yield 3.5mins flights at full throttle.