The 2004 GS500F has been said to have the same carbs as the 2001. However nobody has yet taken apart their carbs nor has one of the major members on this site gotten their hands on a 2004 to verify things. However if you want to expriment you can rejet using the 2001 jetting guide. Let us know if it works out. Pictures with instructions is always handy.
Links:
How to rejet a 2001+ GS500 (http://www.gstwins.com/forum/viewtopic.php?t=12928)
'04-'05
Main = 130
Mid = 60
Pilot = 17.5
Pipe alone, 132.5 main and shim the needle 0.5mm. Bike will run fine without shim.
Pipe and K&N, 135 main, 20 pilot, and shim the needle 1mm. Bike will run fine without shim.