It sounded like it had run out of gas. I pulled the clutch and coasted to the side of the road. Chris couldn't put his kickstand down in the grass, so he just sat behind me and waited. I was glad his bike and helmet were so colorful, to attract the attention of the cars that zipped by so closely. I walked around the bike, looking for something, anything, unusual, then checked the gas, the filters, and the fuel lines.
Vapor lock is a common problem in hot weather.
The liquid gas that flows from the tank to the carbs evaporates in the fuel lines because of the heat. This is not a good thing, because the whole purpose of the carbs is to mix gas with air so that it can be sent through to run the engine. The gas in the carburetors is supposed to be evaporated. The gas in the lines is not. When the liquid gas in the fuel lines evaporates, the two meet at the same consistency and just sit next to each other, building pressure but going nowhere, because there is no heavier or lighter substance to force the issue.