anti backfire valve? (oem carbs)

I was searchiug for available parts for my 87 GL with anticipation. what is the anti-backfire valve? My chiltons does not even list it. the part I found:

http://www.partstrain.com/products/Engine/Air_Intake/Anti_Backfire_Valve/1987~SUBARU~GL~4~1.8~LOY-4WD-001.html

I had an 87 dl that backfired through the exhaust, and now an 87 GL that does it through the carb. Does this valve have anything to do with it? where is it located? The GL is my concern now with cyl heads that have no asv ports, just an egr valve like on the spfi cars. Thanks for help. I was just going to simplify the way it is now, but want to be sure.

EDIT:

Woops. I searched and found it. will use GD's advice.

http://www.ultimatesubaru.org/forum/showthread.php?t=62694&highlight=anti+backfire+valve

FURTHER EDIT:

Hey an item I really liked was the air bypass on spfi - letting off the throttle had no engine smoke, as it kept positive crankcase ventilation. I would like to use the spfi type egr valve open to clean air, open when throttle is all the way closed for clean engine braking. I will restrict it so as to not give it too much , maybe run a hose to airbox with fitting from intake after head is plugged. what vacuum line opens at idle on the carb (if one even exists)? That would really help the pcv and backfires.