This tread has been hugely helpful. Bought a Yamaha Kodiak 350 in 2018 and starting seeing similar problems just a year later. On hotter days after climbing to around 8500-9000 in elevation, and on an incline, with 1/2 tank of gas, I would get the sputtering and stalls. I'd let it sit for a few minutes before trying to start and it would briefly start, but putter out as I would use the throttle. If I turned it around and let it roll down hill, I was able to start it and would run fine. It's completely fine riding anywhere else, but the combo of heat, elevation, incline, and 1/2 of gas seems to be what's common. You'd think Yamaha would have taken measures to fix these issues years ago, but apparently even after these posts in 2012, 6 years later they still didn't resolve much. I took it in after it started happening the first time, and Yamaha replaced some parts at no charge. The dealer said there was a recall and the labor/parts were covered. After fix, I didn't notice issues for about a year, but has returned this year in 2021. I think it was always there, but during the in between year it just so happened I didn't put my machine in those particular circumstances. I'll have to try some of these solutions; 87 octane, StarTron Fuel Stabilizer, keep full tank, new air filter, and if I get time do a heat shield wrap on the gas tank.