My bike is losing power when it runs please help

[Reyji]

Hello,

My bike is still fairly new it's an 08 with 4000 KM. I was cruising around in 4 - 5th gear yesterday when I heard my motor sputtering and then the engine gave out on me. A car almost rear ended me. After a few attempts to start the bike it took a good number of times before it would start again the same situation happened my bike would just die down after the 3rd gear. I know I still have plenty of fuel left because I can see gasoline when I open the fuel tank and can hear the gasoline when I shake it. After trying to figure out what was causing it I turned the fuel valve to Reserve (arrow pointing to RES) and this fixed the problem. The bike runs normally again. As soon as I switched the fuel valve to the ON position the same thing would happen the engine would just sputter and die down. There is enough gas in the fuel tank so I cant be running low on gas.

What do you think could be causing the problem. Is it a good idea to leave the fuel tank on Reserve from now on? Your suggestions and help is greatly appreciated. Thank you in advance.

Rey