Back Firing Alero

I got my exhaust tuned by RSM in toronto and since then i am back firing not sure why. Is it too much fuel or not enough or something else. I would like to get it fixed its pretty embarassing. But the mod is great it pulls pretty good now.

[Fast Eddie]

Its back firing eghh? back thru the carb!! That's not good!!!

[brim]

would be rich, getting unburnt gas into the exhaust pipes

sometimes with a small leak you can feed the fire, under normal circumstances the exhaust gasses coming from the motor cannot be reburned, in rich conditions it can

or i'm just talkin out my ass i'm not sure....