Senior Member

How do you know it is at 'half tank'? Perhaps the guage is misalligned, or the sensor get stuck. 1) find out what size the tank is supposed to be.

Then 2)Run it until it stops 3) Fill the tank 4) Compare the amount put in to the tank volume

OR 2) run it until it stops 3)siphon/pump/drain the tank into a measured container 4) compare the amount removed after the engine stopped with the tank volume

If the guage is accurate, then perhaps something is blocking the fuel line. Sort of like a straw which is only halfway into a drink can't get to the last half of the liquid.