I have an 03 Yamaha YZ450F and I keep frying spark plugs. I put a new spark plug in and I ride for about 30-60 minutes. All of a sudden, when my bike gets hot, it starts blogging and cutting out to the point it quits running. It won't start immediately. If I sit there for 5-10 minutes, it cools off enough for the bike to start right up. I ride it for 3-5 minutes and it does the same thing. I did this 5 times just to get my bike back to camp this last weekend. Once I get the bike back to camp, I put in a new spark plug and it runs like new....for another 30-60 minutes. I have done this 4 times so far. I run a Big Gun CDI box in it and I have also tried it with the stock CDI with the same results. I have read several other threads and can't find an answer that really nails this down. Anybody have any answers for this? Could this be related to Octane of the fuel? I have ready several other threads that four strokes need 91 Octane. Embarrassingly, I have been running 87 octane, per a recommendation from a friend. I won't do that again.