Setting the timing mark on distributor

[storyteller]

I just got my '39 Flatty engine back together and running. Have new carb, rebuilt distributor, new points, wires, etc. It starts at the touch of the ignition starter button, idles fine. Problem: when I rev it up (in neutral) she pops with a backfire through the exhaust. I took her off the car dollys and drove around in my driveway, upon the slightest load it pops quite a bit. Question: which way should I move the setting on the distributor timing adjustment, UP or DOWN a bit?