Various products are available for removing carbon deposits from the combustion chambers.
The typical procedure is to slowly let the intake manifold suck the solvent in at idle. Engine should be warmed up prior to pouring.
Following this, a large amount is allowed to be sucked in and stall the engine.
After a few hours, the car is then run at high RPMS for 10 mins to break off and blow out the de-scaling carbon.
A fresh oil and filter change is mandatory due to the carbon that enters the oil.
Another use of the fluid is to pour it in the combustion chambers and let it soak overnight. The car is turned over with no plugs the next morning to throw out the rest and the plugs are inserted and again another spirited drive. this has been reported to loosen up stuck rings.
As well, some pour the fluid into the oil to clean engine deposits and into the gas tank to clean injectors and combustion chambers.
Common brands are:
Seafoam (available at Car Quest in Canada) Procedure
GM Top Engine Clean (GM part number 1050002) (Cdn Part number 992872 Cleens @$7.02 in Canada) Procedure