I remember as a kid, my dad pouring small amounts of ATF down carb of slant six, keeping idle up, and telling me it cleaned valves IIRC.
When I first got the RV with 413 it hadn't run in years, I put in 6 qt of cheap oil and did a lot of cleaning:
MMO in the intake when hot, and oil, and gas, and every time I shut it down hot I'd flood it with Seafoam then shut it off to cook clean.
After 2 bottles of Seafoam and a lot of MMO it idled smooth, and I put a snake cam down the intake and in a spark plug hole to look; the intake had NO carbon left and the piston tops shined.
