'72 BB consistent muffler explosion
Check the points to see if they are burnt. If so replace the points and condenser. Check the cap for any corrosion, best to use a cap with brass terminals. If reusing wipe out the inside with a clean rag. Maybe even use a blow dryer on the inside. Try more initial timing with the vacuum gauge hooked up to see if vacuum increases also. Maybe 16-20 initial and enough mechanical to have 36-38 total. Have you checked how much mechanical you have now and how much total? If advancing causes engine to ping retard just enough to stop pinging.