I’ve used Seafoam many times to decarbonize coked up piston rings with success.
Get the engine up to operating temperature and shut the engine off. Remove the vacuum hose from the brake booster. Adapt a hose that’ll fit in the brake booster vacuum hose and into the can of Seafoam. Take a pair of pliers and pinch off the hose. Have someone start the engine and bring the idle speed up to 2,000 RPM’s. Now slowly unpinch the hose so the Seafoam gets drawn into the engine. Keep the RPM’s up and pinch off the hose when required to prevent the engine from stalling. Once all the Seafoam has been drawn into the engine, shut the engine off. Reinstall the brake booster vacuum hose. After a half hour has past, restart the engine and bring the RPM’s back up to 2,000 RPM’s. Keep the RPM’s at 2,000 until the smoke out of the exhaust clears up.
Tester