Here is an other cause, inside the gas tank on the suction line is what I call a corn cobb, some sort of a filter. I've had them plug up with gunk and gum from the gas. You can just remove it and add a in line filter. I doudt there are replacements for them, correct if I,m wrong.
May want to get some SEAFOAM and dump the whole can in the tank. May have to change the filters again after a bit though.
Good Luck