Engine set up

I have a 340 with a mild pupleshaft 484 lift cam, electronic ignition, headers aluminum intake Holley 600 dbl pump.

After setting the timing with a light and vacuum removed and plugged the engine seems to idle best at about 12 deg on the before marks of the timing marks on balancer. If i bring it down to 0 degrees it runs rough

this normal for this engine set up?