I have an '84 El Camino w 305, recently tuned, new plugs, Cap, Rotor, Air Filter, and Crankcase Filter, and oil change....has always passed DEQ....NOT now....have tried twice and the HC and CO emmissions are too high for OR DEQ.  I threw in a bottle of Octane Booster for the 2nd attempt and it emmitted more than the first time thru.
  My question I need answered here before I go to someone who stands to make money off my perdicament is:  Does the REAR Muffler on this type of vehicle have anything to do with cutting down on these emmissions?   Because always before when I went thru I had one....but around 6 months ago that rear muffler rusted off of the car....so they are sticking their sniffer I think - into tail end of the main muffler??

PLEASE Advise and Thnaks!

Michael