hard to describe with out pic, but here goes. the housing the fuel filter goes in up inside has a plastic washer that looks like it holds in place a almost a spring like washer that has flaps. mine has part of the flaps under the plastic washer and like 3 are not. i have to use a pair of channel locks to take the plastic nut off that holds the filter on. the first time i replaced the filter i could remove the nut by hand, but now too much pressure. i think this is my under lining issue that it will not hold fuel pressure over night and will leak down where i have to pump it up to prime it from being air bound. i'm pretty sure this is the issue, where it did not have any problem i changed the last air fuel filter. last year when i ran into a common issue with it i ended up replacing the primer pump which fixed it. now when i take the filter off it is only half full of fuel. looking at the parts break does not show these pieces i have described.
There is a strainer on the pick-up tube inside the tank. I would check it. There has to be a good flow of fuel to the filters. Pressurizing the fuel tank with about 3 psi of compressed air is good way to check the flow to the filters. After checking the strainer.
ya i know it's not the strainer because when i had fuel issues that plugged the strainer and to keep cleaning it and then finally drain the tank and clean it out w/ new fuel filter. when it did plug the machine would loose power so it was easy to tell. there is an air leak some where to make the fuel not hold pressure. thanks for the ideas though.
Maybe try pressurizing the fuel tank with everything hooked up. You might see a fuel leak. Maybe not.