We had been having a fuel starvation problem in the upper rpm ranges. I've been tinkering with fuel lines, filters, auxilary tanks and identified the problem to be with the engine. Took the intake off and was planning on getting into the vst and replacing the filter on the hp fuel pump. I also had the F-shaped filter which I planned to replace. Pulled the F-shaped filter between the lp pump and vst first. Inspection of that filter revealed the blockage. Don't know where all that crap came from, the lp pump I guess. We don't burn ethanol. Didn't see any need to get into the vst. Did a test run shortly after and was very pleased to have solved the fuel issue. Thought I would pass this on to those who might have a similar issue. Now I can get back to fishing!
It's always good troubleshooting to check fuel lines, water separator filters and particulate filters first, but once you're past that you're looking to the LP Fuel Pump Filter and VST Filter. The LP Fuel Filter can be installed incorrectly so pay special attention when removing and replacing it to get in installed properly. I also recommend replacing the VST filter (AND the VST GASKET) at the same time.
When my F250 motors were at about 390hrs I had a fuel feed issue and troubleshot up to the LP Fuel Filter. The mechanic I hired came out and replaced only VST Filter claiming E-10 fuel was the culprit. Two days later and the symptoms improving but not gone I asked about the LP Fuel Filter. "We don't change that until 500hrs" came his reply.
I pulled towed the boat to the driveway and replaced the LP fuel filter on the suspect motor and then spent 1.5hrs replacing the two filters (LP & VST) on the other motor. No problems since.
Parker 2820XL with twin Yamaha F250 motors.