Intermittent symptoms are the worst! They're tough to solve because you usually get stuck at the very first step, confirming the complaint. I had a Honda scooter on my rack one time. The RO (repair order) said the customer complained the bike would run for a short while then peter out and stop. But I couldn't get the machine to do it, or anything bad at all! Five test rides later I was scratching my head. I went on to test fuel flow and spark and ignition timing, even though I hadn't yet duplicated the complaint. All good. Then someone happened to mention that the rider was a very large individual, possibly a bit bigger than the scooter was intended for, maybe nearly 300 pounds? And then it hit me. The seat base on this machine was like the seats on many smaller bikes made of plastic. I could easily envision it bowing quite a bit under a considerable load. And where was the fuel tank, with its vented cap right on top? Yup. Almost dead center in the underseat area. Looking for marks on the seat pan, I detected the outline of the cap, sure enough. Figured I had it solved, and by loading up two mechanics on the seat for an in-shop test, I confirmed that was what was happening. Happy to have solved this one, I prepared my notes on the RO. But I couldn't help feeling sorry for my service manager. I mean, my part was easy. Can you imagine trying to explain the problem to the lady that owned the bike?