Fuel pump want shut off

Hi
I have twin Yamaha four strokes 225 hp from 2002. My low pressure fuel pump on starboard engine want shut off. Engine starts but it is back firing on me when I increase power. Can anyone help me with this? Pump is okay. Fuel filters clean, wiper separator filter clean. High pressure pump gives out 50 PSI

[boats.net]

Backfiring is usually a timing issue or ignition problem. Check the belt timing and check ignition timing.