What is wrong with my pit bike?

The pit bike runs for 15 minutes sometimes, other times it only runs for 5 minutes. Then it bogs out, like it is running out of gas, but it always fires right back up. It is a 125 Orion and I am having a hard time figuring out what is wrong with it. The carb is clean, the float isn't sticking, the tank got cleaned and the fuel valve was cleaned. I thought it would be the cool but it always starts right back up. Someone please help.
The Pit Bike runs for 15 minutes sometimes, other times it only runs for 5 minutes. Then it bogs out, like it is running out of gas, but it always fires right back up. It is a 125 Orion and I am having a hard time figuring out what is wrong with it. The carb is clean, the float isn't sticking, the tank got cleaned and the fuel valve was cleaned. I thought it would be the cool but it always starts right back up. Someone please help. I have checked the gas cap and it is vented. Changed fuel lines because it was collapsed and it is a 4 stroke.

Gas cap is not venting properly causing a vacuum condition in the fuel tank. Check the cap. I do not advise this but leaving the cap a bit loose so it allows venting into the tank as a test will show if this is the problem. It is dangerous and possibly violates emission regulations so don't do it on my say so but...