How do iget the fuel gauge on my 2002 aprilia 125 to show up,

Hi there can you please help me with my problem i've got aprilia sx 125 61 plate i've been to 2 bike shops and they could fix the problem i tic over at 1500 for a bit then it drops to 1200 then 1100 then 1000 then 900 then it just dies out and when i'm give it some 50 60 and comin to lights and grearing down to neutral it revs very high and the to get the revs back down i've got to pull the choke in to bring the revs back down can you help me thanks lee

There aint one m8 i have the same bike same year and no petrol gauge only earlier rs had them they swapped it for a sidestand switch