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"Blowing out the carbon"

Did that ever really work, back in the carburetor days? Could it work now? What was it that worked, in this story, below, from my brother in Boise?

Remember Bill Cosby’s routine about his car that was guaranteed to be able to go 200 mph[*]? He took it to his mechanic when the engine was running poorly, and the mechanic told him he needed to blow out the carbon, so “Take it out and drive it 100 mph in second gear.”

Well, I thought of that when I was pondering how to fix my aged van, so I took it out and drove it 50 mph in second gear. Now it’s running smoothly.

The car is a 1993 Mercury Villager, only one engine made–I think 150 cu in 6 cyl. 175,000 miles. New plugs. Usually sits for 7-30 days between uses. Then only short trips of less than 20 miles and rarely over 45 mph. Don’t know what was gummed up, but I just did what I could to get the RPMs up for a while.

*From Art1966: As I recall, Cosby’s line was “I need a car that goes 200 miles an hour … to get to work!”

Yes, I still have Cosby’s “200 mph” routine in my tape archives. He did it back in the '60s.

The car in question was the Cobra. When Cosby asked the mechanic where he could go to drive at the recommended speed, the mechanic’s reply was “Any side street.”

I loved that routine. Haven’t played it in years. Have most of it memorized.

If it has carbon build-up, there is something wrong with it. It could be bad injectors, or a bad air/fuel mixture, or bad ignition. In any case, if “blowing out the carbon” helps it run better, something is wrong and a proper diagnosis and repair is probably in order.

I’m with Whitey on this. Sort of.

Back when Bill Cosby did that routine engines were carburated, ran rich, and could build carbon deposits in the cylinders if only used for short trips. Modern cars meter fuel far more effectively and in a manner more condusive to complete combustion. And they run hotter. In the '60s most thermostats were 165F, today they’re 195F. That increase in temperature was implemented in the early '70s as on eof the early emission reduction steps.

In short, modern engines should not build up carbon as readily as engines did when Bill Cosby did his skit. However, if the engine is high mileage and using some oil, and/or used for only short trips, it can still collect carbon. When an engine is cold, its ECU bypasses the oxygen sensor signal and allows it to run rich until it warms up a bit.

Bottom line: while modern engines are less prone to carbon buildup than the engines of old, they are still not totally immune to it. But if when changing the plugs you discover really bad buildup, or if one plug looks dramatically different that the others, you’ll want to check things out, starting with a compression check. It sounds from the post like yours is running normally for a higher mileage engine, but if you’re curious you could always run a compression check.