My Onan marquis Gold 5500 on a 2007 model Intruder is doing the exact same thing. Runs 15 - 20 minutes and quits. Very hard to start after it quits. Spray some WD40 down the throat while cranking and it will fire. It has always done fine before today. I just started researching.I appear to have the old style fuel filter that attaches to the carb. It may be original, I don't know, I'm not the original owner. I'm thinking I will replace the filter( maybe with the adapter and inline filter?) and see if that eliminates the problem. And I'm going to see if I can locate where the fuel pump is so I can replace that if need be. I need to do more research.