THERE IS A PRODUCT MADE BY SEAFOAM IF I REMEMBER RITE CALLED TUNE UP. IT SMELLS LIKE PB PENATRATING OIL, THAT YOU SHOOT INTO ENGINE THROUGH PLUGS AND TURN ENGINE OVER THEN LET IT SIT, HELPS FREE STUCK RINGS. WE USED IT ON 2 STROKE BOAT ENGINE, IT IMPROVED COMPRESSION TEST RESULTS TO WITHIN SPEC. DOES NOT UNDO RING WEAR JUST FREES RINGS STUCK BY CARBON AND VARNISH