Do you have a full 12v going to your HEI. HEI didn't come out until '73 as an option,and on all in '74, (pretty sure). Your '72 came w/points originally. Shoot your power wire for the didtributor, should be a 12g wire with 12 volts w/the ignition on. If it was converted and is stiil using the small resisted wire originally used with points (6 volts), your HEI will not work to it's full potential. Check this site for further insite.
http://www.oldengine.org/unfaq/hei.htm
Hope this helps!
