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We used to use a Binks #7 commercial spray gun (for painting cars) and water to remove the carbon in Nissan Z car engines. The 81-83 models had a combustion chamber design that had about 33% of the piston top (flat top piston) within 1 MM of the cylinder head. When enough carbon accumulated there it would sound like the engine was coming apart.
Used vice grips to set the throttle at 2k RPM and sprayed the atomized water into the intake. I know it worked and many of my customers did not have to get it done again for years.
No need to change the oil, although we usually did it after we had confirmed the carbon knock was gone. We could look through the spark plug holes to see the piston tops, but the carbon knock was the reason we did the procedure.
I once towed a car 180 miles with the customers approval to replace the engine, and fixed it with this process in less than an hour, without disassembling any part of the engine other than the air cleaner assembly.
I do use BG 44K, but only about once a year. Newer design fuel injectors seem to have minimized the old spray pattern issues with the early pintle type injectors. Ethanol probably helps some also.
regards
Mech
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