Pinging

He did say he has 30 degrees mechanical with light springs didn't he? I personally would limit mechanical advance to 20 and set initial to 14. you can go up some and see what happens but alway go down 2 degrees from ping to comp for extreme temps. If you are running vacuum that is most likely your source of detonation. Mine actually started to buck and loose speed when the throttle was returned to near closed from a moderate to aggressive acceleration. (unhooked vacuum hose, plugged it an drove home). Most cans will have at least 16 degrees under light throttle and some as high as 30!