I have a 68 Camaro with a ZZ3 350 engine. It has a Carter carb. I removed the Mallory dual point distributor and put in a Hi-performance HEI distributor. I used the hot wire of the firewall which looks to be 12 gauge. I set the timing to 8 degrees BTDC. It idles great but lags and backfires on hard acceleration. I advanced the timing to 2 degrees BTDC and it improved but still won't take hard acceleration. Do I dare advance the timing? There is no pinging. With the timing light connected I can see the vaccuum advance working. Any ideas?