1996 Honda Civic smells and smokes while warming up

1996 Honda Civic mileage: 107,000. I recently had a valve job done on my car. Now the car is emitting smelly smoke while I warm it up. What does this mean? What can I do to reduce this heavy, stinky smelling smoke? I told the Mechanic and he claims that because I ran it on three cylinders for so long that there is a carbon build-up on the Catalytic Converter. By the way, my car is carbureted.