Read here: https://forum.tinboats.net/viewtopic.php?f=4&t=39239
For the record, Seafoam isn't abrasive ... but whatever carbon may come out of a cylinder could be (regardless of engine tuner solvent used, just so you know), so heed strongly Pappy's advice in the post above about adding extra oil for whatever treatment method you use.
Otherwise, I have been using Seafoam for 30-years with zero issues. It was even invented for use on OB motors when the fuel/oil mix was 16 to 1; in fact it was presented to none less than ol' Ole Evinrude himself!
And besides use on OB motors, I have resurrected from the grave many a small motorized piece of equipment, 2 and 4-cycle (lawn mowers, chainsaw, pressure washer, weed trimmers, etc.) that were given to me and all were not starting or running whence received. Seafoam is a big part of my success in getting them operational.
I even used it to clean out my old Ford Explorer and the engine ran much smoother afterwards and my gas mileage increased!