Like others said....check your timing, idle speed and idle mixture.
Set your total timing to not more than 36 degrees with vacuum advance blocked off. If you are running a healthy cam(which you should be with a 347) disconnect vacuum advance and get your distributor recurved.
I assume you are running a Holley carby. Set your idle mixture by turning the adjuster screw on either side of the metering block in clockwise until runs rough then turn it out half turn. This is just a rough guide and should be done by someone familiar to tune them.