In the summer, mine (325 EFI) will sometimes start running roughly and die out; I'm pretty sure it's vapor lock. The early models all had this issue, and Kohler came up with an updated fuel pump to fix it. The tank vent was another issue on the early models. I"m pretty sure my memory is right on this stuff, but if you want details or verification, I'm sure a call to the Miller tech line will get the info you want.
I can make mine run properly by opening up all the doors and letting it cool for 5 minutes or so, then running it with them open. This has happened to me twice this year so far, and both times the issue was completely fixed by running with the doors open and it ran properly for hours afterward. I'd imagine the heat problem would be worse yet if a person had their machine in an area where it didn't get good airflow all around it.
Mine has over 1000 hrs on it.
Another thing to do would be to make sure you've changed BOTH fuel filters recently. And as mentioned above, there's a max fill line on the tank and it shouldn't be exceeded. That said, I had done all of this stuff and still had the problem.
