What can be the problem if the fuel gauge says

You must replace the fuel level sending unit, it is not repaired.

This is caused by a defective fuel level sending unit inside the fuel tank.

Sending unit gas gauge in the gas tank has gone bad and will need to be replaced. The gas gauge wire is grounding out causing you to have full full indicated and when there is no ground you get empty signal.

This is caused by the gauge in the tank having a bad spot on the float, which is common from wear and tear. Also if your lucky, it may just be the wire harness from the gas tank to the frame might be the issue and will need to be replaced. It worst, it's going to be the sending unit it self.

Thank you for using fixya and good luck

the fuel level sensor in your fuel pump has gone bad. it is intergral to the entire sending unit assembly (fuel pump), and is located inside the gas tank. you must lower the gas tank to gain access. good luck!

this almost certainly is the sending unit. the fuel tank has to be removed to change it, as it is in the tank.

not sure what the hell that means, but if your fuel gauge is moving around then you probably need a new float. It's located inside the gas tank and usually part of the fuel pump. Not an easy job, but possible...

You weren't low on gas - your fuel tank sending unit is failing and needs replacement. It's inside the tank and usually can be replaced without replacing the fuel pump as well - don't get suckered into that.

in your tank thers a float it could be sticking failing that the clock is faulty

Put the gas in the tank, let everything settle, turn key off, then back on to on position, but NOT start. Let the fuel relay engage the pump and draw some gas pressure. Give it a good minute and it'll start right up.