I fired up my 63 Lark 259 canadian V8 after replacing the electric fuel pump this AM. Engine has a AFB 4BBL from a GM application, source unknown. This has not yet been on the road. It starts, idles and runs well, but it had an intermittent exhaust back fire from both banks but primarily and most frequently from the drivers side. It runs and revs fine with no load. When in gear the back fire is more frequent but not constant. At 1500 to 2000 rpm with no load it's either gone or no longer noticeable. the fuel pump is an inline 35 gph at 7 psi max. Turning the dist to change the timing does lese it some but doesn't clear it up. Plugs are new, points cond and rotor are what was i there when I got it points and rotor look good, cap looks good with no visible carbon tracks. It has those yellow "performance" plug wire also. Coil operated at normal temps. Ran it for about 35 minute got it up to 190 degrees. Any ideas appreciated.