Strange Pinging, incorrect vacumm advance??

[grayw0lf]

Hey Guys,

I've been hearing a strange pinging while driving around my '70 C-10. I have suspected it to be detonation, as the previous owner set the timing strictly by ear. I disconnected the vacuum advance & plugged the hose at the carb side.

(Should I have plugged it at the distributor side as well?) I don't know the exact timing for a 305 from an 84 Camaro w/ HEI, but I figure its between 8 - 12 degress BTDC. I set it to about 10.5 btdc. I reconnected the vacumm advance & it immediately went to about 25 degrees (possibly more) btdc at idle in Park.

Is this normal, or could this be my culprit?

Thanks,
John
P.S., I swear to the Lord above that it had a 305 when I bought it!