Probably need to properly, thoroughly clean the fuel tank.
My guess is there's an ugly crud in the tank.
Best to remove tank,as it allows you to aggressively 'slosh' cleaners ,up down all around to remove whatever is inside the tank clinging to the walls.
Depending on the tank you may be able to remove fuel sensor and get a 'fan/low pressure' power washer head inside,maybe.
Yes, removing the tank can be a pain( 'fun' on my BX23S ) BUT it allows you to better clean and inspect.
After you clean with water, blow out with compressed air then use winter windshield fluid as a final 'rinse', blow out again.