Plugs, points, and condenser, set dwell and timing, check advance, then adjust the carb for idle mix and speed, all as regular maintenance done every 12,000 miles. Back in the sixties when we started working on cars, this was the gravy job. That doesn't mean the car will actually run like new, however.
Stuff happens out there in the harsh real world.
You simply can't squeeze thousands of gallons of complex liquid hydrocarbons through .002 in. With the average age of our national fleet heading for 10 years, more and more motorists are now experiencing those consequences in the form of starting and driveability trouble. People started to recognize this back in the mid '80s, and there was a flurry of excitement in the aftermarket about injector cleaning. Finally, something to replace the business lost when we got electronic ignition, unleaded gas, EFI, and computerized engine management. The oil companies and the car makers weren't oblivious to the issue, however.