If you have done the filters about the only thing left in the system is the inlet strainer in the tank. If you have an air compressor try this.

Take the filler cap off the tank, disconnect the fuel line from the tank at the primary filter, blow air back through the line into the tank, get someone to listen at the tank filler to hear if the air is really coming through or just barely bubbling. If it is really coming through you may have either blown off what ever was blocking the strainer or the falter may be clean.

I have also put air pressure onto the filler neck and blown fuel towards the engine. This way you can see if you are getting a full flow. Don't get carries away and seal the hose into the tank. Just wrap a rag around it. You only need a pound of pressure or so.