6 pak run bad cold

advancing the timing is not a bad idea but you need to limit the total advance in the dist. do a re-curve. when you block the heat riser you need to set your idle circuit a little rich when hot to get it to idle when cold. or wait for it to worm. if this is something new i would say you have a vacuum leak or cam timing is some how off or blockage in thee idle circuit in the carb.