Exhaust backfire

[66DARTGTMAN]

Hello

I just finished installing a new Summitt carb on my 66 dart with a 383 in it. I have to crank it a lot and it will fire when i let off the starter. Then it wont idle I have to keep the rpms around 1500 to keep it running. Anything under 1500 and it wants to die. Could this be timing or the air/fuel needles on the new carb. What would be a good start for the timing degrees. Am I correct in thinking that the backfire is unburned fuel in the exhaust.
Thanks in advance

 

[oldkimmer]

..........if it ran reasonably well b4 most likely not timing.........sounds lean..........is there a threaded plug in the back of the carb, or do u have a vacc hose to the brake booster....is the electric choke sticking closed...kim........