It appears the FMS is not counting fuel in the "Center2", "Center3", "External1" or "External2" tanks in this CS C130 configuration:
Aircraft.cfg Fuel Section:
External1=  -0.75, -25.49,  -7.03,  1400.00,   10   // EXT Left 
LeftAux=    -0.75, -25.49,  -2.03,   910.00,    9   // Aux Left 
LeftTip=     0.00, -16.86,  -2.09,  1350.00,   10   // Tank 1	
Center2=    13.64,   0.00,  -4.19,  1240.00,   10   // Tank 2	
Center3=   -20.95,   0.00,  -4.19,  1240.00,   10   // Tank 3	
RightTip=    0.00,  16.86,  -2.09,  1350.00,   10   // Tank 4   
RightAux=   -0.75,  25.49,  -2.03,   910.00,    9   // Aux Right
External2=  -0.75,  25.49,  -7.03,  1400.00,   10   // Ext Right
The Center2, Center3, External1, and External2 are missed in the SMITHS FMS Perf Init Fuel load (FSX shows I have 30,485 lbs of fuel and the FMS shows only 12.4 thousand lbs).
I believe the complete list of Microsoft simulation tanks are: Center1, Center2, Center3, LeftMain, LeftAux, LeftTip, RightMain, RightAux, RightTip, External1, External2.
Or, you could simply read the combined total fuel weight directly from the flight simulator (simulation variable FUEL TOTAL QUANTITY WEIGHT in 
http://msdn.microsoft.com/en-us/library ... ftFuelData).
Any help would be greatly appreciated!
Thanks,
Jason