We have a SBC 350 in our street rod. It is pre-electronic ignition, so it is probably a mid 70's version. Problem is that when you shut engine off it wants to run on and jump around. We pulled plugs and they do not appear to have a lot of carbon build up, timing is set at about 12 degrees. Problem seems worse when engine is hot, if you shut it off in gear it will act normal? Any suggestions would be appreciated.... THANKS... THERESA