Primer bulb

[Airslot]

Sometimes a primer ball will go bad. If the check valve sticks then the ball can get sucked flat. It could stick in a half open position and cause your problem where it gets enough fuel sometimes. If the ball is getting limp, replace it with an OEM ball, not a tempo or cheapie aftermarket ball.

Airslot
Could also be a fuel pump going bad but I'd replace that ball first.