A. There are actually 3 different emissions systems on the Viragos, depending on the year and size. Below I've listed what is on each model, and where it's located. Disabling the AIS system on some  models seems to stop the incessant back-firing on deceleration. This does not mean disabling the "Coasting Enrichener System" on the 1988-on XV750 and XV1100 models. 
More Information:
The three systems are the above mentioned CES on the 1988-on XV750 and XV1100 models, The "Mixture Control Valve" on the 1981-1983 XV750 models and 1985-1985 XV700 models, and the Mixture Control Valve and Air Induction System on the 1988-on XV750, 1984-on XV1000, and XV1100 models.
The AIS system and MCV systems can safely be disabled by disconnecting the hoses that go to the valves, and re-routing the vacuum lines to exclude them from the system. Both of these modifications are effective at reducing and in some cases eliminating the back-fire that plagues the Viragos on deceleration. 
Comments: On the 1981 to 1983 models, the MCV valve is located on the left front side of the frame under the engine mounting bracket cover (that cool air-scoop lookin' plastic thingy with the gaudy amber reflectors on it). On the '84 and '885 XV700, it's located in the left side pod, or "bug eye" funny looking chrome cover. I have removed them from both of my bikes, stopping the backfire on both, and the bikes have suffered no ill effects.  For those of you with '86 and newer bikes, your MCV and AIS are both located in the left pod cover as well. They are easily disabled, and if you do it, you won't regret it. However...if you live in a state that insists on making you go through those ridiculous emissions certification tests, you'll want to leave it intact inside the cover so you can reconnect it annually for the tests. For those who don't have to have emissions tested, you can now do away with the left pod entirely, or at the very least gut the thing and just leave the pod empty.

Click here for images of the AIS on 1984-on Viragos