Popping/backfiring through carb. Help?

[dmw319]

So one day my truck runs fine and the next its popping and backfiring through the carb (I can see it when I take the air cleaner off) and its loud!

70 c10... 350 motor, 1405 Edlebrock carb, HEI distributor. Plugs/wires changed about 2 years ago. Running 4.5lbs fuel pressure through a mr. gasket regulator. It appears I may have a slight fuel seepage from the pump/fuel line connector so I'm going to check the pressure on it tomorrow night and make sure its not the culprit (its pretty slight, and been this way for a while). My timing was set to 20 degrees, which I thought was a bit high, so I took it down to 12 but still having the issue. It starts really rough (have to pump the gas a bunch). Once it starts, it idles OK, but driving it seems like its misfiring and not responsive at all when I press the gas and bogs when I'm not giving it gas. So, I have just been letting it sit the last 2 days.

Any ideas what could be causing this?