I have a 1968 Ford F-100 shortbed i pulled the 360 4speed out and put in a 390 with a C6 when i start it it runs really ruff @ idle and when you slowly push the accel down it starts popping out the exhaust and sounds like its missing. i have the distributor on TDC and on the right slot on the cam but its just dont go away no matter how much we time it or mess with the carburator if you just hit the throttle and let off it does fine but just driving or trying to take off its nothing just pops and backfires im running out of idea of what it could be there arent any vaccume leakes and the wires are fine coil will be replaced tomorrow but other than that im pretty much blank on what it could be. any ideas would be very welcome!

 

What do the plugs look like?

Do a compression test yet?

Put a vacuum gauge on it?

What is the total advance, and when is it all in?

Did this 390 run before you installed it?