[bigblockv6]

Back in the 70's GM had what they called " Top Engine Cleaner" that you could by at the parts department at most GM dealerships, designed to clean up the top end of the engine. I used to use this on my 68, it was thick as molasses , you would start the engine and pour it down the carb and let run for less than a minute then let it sit for about ten minutes and then start the process again. It really put out a strong smell of ammonia but really did the job of cleaning up carbon. If there is anything similar like this out there today it would be a good idea for engines that have carbon build up.