I'm trying to figure out why my 56 Customline has developed a run on problem after I turn the key off. I do have a new MSD Street Fire ignition box, but I don't think that is the cause. I double checked spark timing today with the engine warmed up and the vacuum from the distributor plugged and I am right at 12 degrees BTDC with engine idle at 800 RPM. The car runs fine at all speeds and the spark plugs look like they are burning fine. Any ideas? 

  Ron Lane,  Meridian, ID