I just put a weber card on my 87 jx with the stock 1.3 and I drove it over the pass and backk on one tank 200+ miles but filled it up again and im NOW at 72 miles at half tank? It seems like if im constantly driving I get 19-23 mpg but when i run to school then 6 hours later come back to run home my guage is lower than when i left it. Tank is dry!!! but if i were to go fill it up it seems as if the guage is always acurate! HELP!! mile counter seems acurate as well

My 2 ideas on "What's a Happen' Here"!!

1st, if you have the stock fuel pump, the return line is running Warm Gas back to the tank.
      Gasoline is a VOC with a boiling point at 104 degrees, ie. IT EXPANDS LIKE KRAZY !!
      And it contracts like wise. "Different readings after being parked."

2nd, Any fuel gauge is a "Estimator" at best, Also your tank is not of a perfect shape for volume,
       and the gauge "Sender" measures "Fall" from top to bottom. Visualize a Round Fuel tank like on
       a Semi Truck, as the fuel is being used, it goes down slow to the 1/2 way point, then it seems to
       just "DISAPPEAR" in  the lower half. Also at 3/4's, the amount used IS NOT A TRUE 1/4 of the volume.
      This gets many "Truck Driving School Graduates" on their first trip out ! Even new equipment operators will get caught
       Running Out. I have made many a times a "Never Fails Fuel Gauge" to help a NEW GUY OUT...
       A surveyors slat, with 1 inch marking to the bottom of the stick, nothing beats a Gas Tank Dip Stick !!!

CAPT

But like I said if I come back to my car how ever many hours later the gauge will be lower. But if I were to go to the gas station right then and fill up The gas gauge would be considered acurate. So Somewhere Sometime while being parked I am loosing physical gas. Like this morning I started her up. Had just under half tank. Drove 10 miles to school. came back 2 hours on my break to get coffe and my guage was now at just over quarter tank. So I drove right to the station and filled it up and It was just over 7 gallons.

I have no idea what conditions are where you park but it is easy to siphon gas from a Samurai.  Just a thought.