antisiphon valve
 

On an 86 cudy with the belly tank were would the antisiphon valve be located?

That should be it right there, doubtful it was replaced.
Here was mine off the saddle tanks.
http://i175.photobucket.com/albums/w...Picture065.jpg
http://i175.photobucket.com/albums/w...Picture075.jpg
http://i175.photobucket.com/albums/w...Picture074.jpg

Thnx I removed the hose barb on mine it was brass I thought the square part was part of the tank when i go out to the boat this weekend i will try to remove the valve. The one i bought i will have to return because it will not fit.

What is the object next to the valve sitting on top of the tank?

That "was" the filter screen.
Depending on the tank manufacturer, the fitting may be pressed into the tank and almost not removable. See if the hose connection unscrews from the tank fitting, that should be the anti-siphon.
You may have a screen filter in the tank at the end of the pickup tube.