My bike has done this a couple times where it sat for a while then wouldn’t start. Would spend days trying to kick it over then eventually would always get it to start, then after that it would start perfectly every time. I just put new piston in and it ran great before and now I put everything back together and it’s not starting, been trying for a couple days. The valve clearances and timing is all perfect minus I just checked the ignition timing and it seems to be off a bit. Just weird why it would run perfect before and only be trouble to start once in a while. And now that I took everything apart and back it’s doing the same thing. I put new spark plug in that’s good. I even put fuel in the spark plug hole to see if my fuel filter was gummed up or something. If my ignition timing was the problem I couldn’t see how my bike would run perfect before and only not when it sat for a long time. I’m thinking about replacing fuel filter before giving up and taking it to the shop so any advice would help.