hey guy's my 2 cents. i race full size outboard drag boats, i use a product made by o.m.c. called carbon guard. mixes with your gas and no more carbon, only leaves a slight brown color on top of the piston. carbon is the number one killer of outboard motors, it gets behind the ring and grows until the ring grabs a port. so naturally i run leftover gas from my boat in my airplanes which is pump 93 octane, klotz oil and carbon guard. i get comments from fellow racers during our tear downs about how clean my motor is, well thats the only thing i do different from them. my piston will look like it comes out of the box other than the light brown color on the dome and theirs will be coated black. so the proof is there in a side by side comparison. we all run the same gas and oil.
yamaha calls their version "ring free"
cant remember what mercury calls theirs.
you only add one ounce to ten gallons so a bottle will last years, but i usually double it, don't see where it would hurt. jeff