Fueling from cans is one source of problems. My uncle was particular to use a brass screen funnel. He showed us one day that the brass would prevent water from getting through when gasoline was already flowing. It also trapped flakes of???, as they tried to get into the tank.
How old is this fuel?
What was in the can earlier?
Is it rusty inside?
Condensation in the can?
Is there residual flakes in the tank?
Will sufficient fuel flow from the sediment bowl when the glass is off of it?
Keep thinking!! Jim