What I do is add a 1/2 can of Seafoam in a gallon can when ever it runs rough then draw from that can instead of the main tank and exercise the genset under load for an hr. My genset rarely gets used and I have to look for ways to use it rather than exercise it for an hr each month. Two other things I would try is whenever it shuts down while it is still hot, check the spark I have had to replace my coil because it would not work when it got hot. The other thing to check does the fuel pump still pump gas when it shuts down. I had a loose hose clamp on top of the main tank than was loose, sometimes it would pump fuel and sometimes it would not. I ended up replacing the rubber line because it was 25 years old sometimes they can leak air due to age. Good luck.
