Backfire and Deaccel Valve

[Germain]

I was wondering if anyone knew exactly what the deaccel valve does, and why. I have seen the chevy used them to reduce backfire on Chevettes. I'm wondering because I have removed mine, plugged all the holes, and had the car make an awful loud backfire with cool black smoke. I checked everything I could think of, but no luck.

This is what I could think of
Timing
Dwell
Valves (Exhaust) not opening
Fuel Pressure

Well, thats about it. Any ideas what might be wrong? And anyone got info on the Deaccel valve? Thanks

Germain