I noticed that when the bike have been running for a while and I shut off the bike it becomes hard to start it if not impossible
Do you mean that stopping and immediately starting again is difficult, or is it when you stop it, leave it 10 minutes, then start again?
If it struggles to start after several minutes, that could imply a fuel issue. A hot engine does not want choke, and does not want a rich condition. But after sitting for a few minutes with a hot engine, the carb floats will be full and the extra heat will help vaporize it, making a rich condition. Most carb bikes, even when running properly will have more trouble starting when hot for this reason. But a carb service can usually improve it - making sure the fuel tap isn't leaking and that the needle and seats are sealing properly, and most importantly the float level.
