73 grand am popping out of the exhaust

[73GrandAm]

Hey guys this is my first time ever going on a forum
Im having trouble with my car it's a 73 grand am has
A 455 , mild erson cam,750 edelbrock carb
,hooker headers. It's popping out of the right bank
At low rpms and at idle it idles around 1100 rpms
If coasting about 30 miles it sputters and pops only
Out of the right bank but if I put pedal to the floor it
Accelerates fine and quits sputtering and popping
I have changed plugs , coil, distributor , wires, cap, rotor, the timing is 12 degrees advanced if lower won't run well .
I checked the rocker arms for slack but fine the travel
Of the rockers looked fine valves opened fine.
The only thing I can think of is checking the pushrods and lifters?
I'm at a loss guys . Any suggestions will be greatly appreciated.

 

[melsg5]

if you have a mild cam there is no way your idle should be that high. THe primary throttle blades will not sit in the correct position with respect to the transfer slots in the carburetor. If your car is an automatic the idle in gear should be 700 to 750. A manual transmission should be 750 to 800. Once you get the idle speed down adjust the mixture screws per the instructions that came with the carb.