During the Korean war when virtually all the high-grade gasoline was being used to make aviation fuel, cars had a chronic problem of getting massive carbon deposits in combustion chambers due to the poor quality gasoline that was available to the general public. The fix was to run a metered drip of "top cylinder oil" into the intake manifold through a tiny piece of copper tubing (1/16" outside diameter) from a 1/2 gallon glass jug mounted under the hood. There was a needle valve similar to a carburetor mixture needle to control the oil flow. Various "pour through" concoctions were also used, like "Casite Tune-Up" and "Wynn's Friction Proofing". My father's shop sold and installed those top cylinder lubricators, and the oil used in them. A favorite product around the Nashville area was "Aviex top cylinder oil". He sold many gallons of it during the mid-1950's.

A "Shade Tree" carbon blast job could be done by running a fully warmed-up engine at around 2500 RPM and slowly dribbling a 6-ounce Coke bottle of water into the carburetor throat. When the water hit the combustion chamber it flashed to steam and cleaned out the carbon.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!