Fuel Gauge Stuck

[philwhite]

Hi Guys,
 
Bit of an odd one, filled up the car last week and after about 100 miles the gauge hadn\'t moved any lower than 3/4, hmm, good mpg or broken fuel gauge I thought? Its an RX7 so the latter is almost certain!
 
Tonight I decided to put some more fuel in and see if the gauge moved, and indeed it did, it showed full as per normal, BUT after 30 miles I can definatly say my gauge is stuck! It seems it goes up but not down?!?!
 
Anyone else had this issue or have any ideas how I should fix it.
 
Phil.

[philwhite]

Sorry chaps, forgot to mention thats its an FD!