Engine Stalling

I just got off the phone with my brother in law. He is out at Pismo with my quad right now and told me of 3 issues it's having. The most important is that when he is going down hill it some times cuts out. He said it's completly random. I was maybe thinking TOS but any other ideas? It acts like it just runs out of gas.

Second is he said it is having trouble starting. He said it happens most the time when it's hot. Trys to start it and just click, like a dead battery. If he turns the key all the way off then back on though it starts back up normal. Is this normal?

Third he has been drag racing a 2005 YFZ 450 and been losing. They are switching off and the YFZ keeps winning. I'm thining WTF since the 05' is a 439. All he has done to it is a Dubach pipe, K&N, no lid, and jetting. I know that's all he has too, good friend. They are telling me who ever gets the hole shot wins the first half but the YFZ has more top end. I'm confused...