I'm having some issues with my 1984 model 316 with the 16hp Onan. It started out with a sputtering issue that has continued to get worse. I had just changed the check valve, plugs, air filter, and fuel filter for the mowing season a few weeks earlier. I've removed the check valve and fuel filter and still have the issue. I've also now changed the fuel pump. It sputters about 80% of the time but then on occasion will purr like a kitten. Anything else to try outside of replacing the carburetor or having it rebuilt? I also always use 100% gasoline and use Star Tron fuel treatment. Any help would be appreciated, thanks!