[MacGyver]

Years ago as a young service advisor I used to work for an AMC Jeep store. The 258 sixes were notorious for carbon. We would actually get vehicles coming in the drive that sounded like they had a horrible rod knock due to enough carbon on the pistons that it would bang on the underside of the cylinder heads. There was a "seasoned" tech that would roll the throttle up mid way and slowly pour water in the carb as the engine was running. This would "steam clean" the cylinders he said. It worked but be very very careful as you know what Hydrolock is. True story but I am don't recommend it as a cure. Currently the best way I have found to safely reduce cylinder carbon is a product called 44K in the gas tank. I have used it personally with measurable results. Another method is GM top engine cleaner. This is poured into the combustion chambers, let set, cleared than started up. It does a good job on engines that ping due to glowing carbon induced pre-ignition.