Join Date: Sep 2000
Location: Washington, Michigan USA
Does it have the A.I.R. system still on it? When the diaphragm in the diverter valve fails (or isn't getting vacuum), it dumps air into the manifolds all the time, which causes constant backfiring on run-down. If that's not it, I'm e-mailing you a procedure for adjusting the valves on a 30-30 cam (which requires a different process than any other solid-lifter cam). Set them per the process, set your total timing (no vacuum connected) at 32 degrees (ignore whatever the base timing turns out to be), and let us know how it runs.
'69 Z28 Fathom Green