Had my bike out in the hot sun the other day (32-35 degC), and it started leaking petrol. The tank was about 20-25% full (so lots of air volume), and the bike was in full direct sunlight at about 11:30am, and had been since sun-up at 6am (southern hemisphere high summer). Thinking that it was a pressure-related issue with fuel leaking out the overflow pipe, I opened the petrol cap, and got a huge swoosh of positive pressure. The engine had been off since the evening before, so no residual running heat.
Anyone got any ideas about the cause (other than hot sun, of course). I would have thought the bike could handle hotter conditions without problems. Kinked breather pipe maybe? The leak stopped as soon as I moved the bike into the shade, and had released the pressure from the tank via the filler-cap.