run a good fuel treatment every other fuel tank. I been running lucas oil complete treatment. its 10 bucks at auto zone. treats 100 gals. follow the amount witch i use a shot glass. its over kill. but doesnt harm. its cleans the carbon. lubes the upper cylinder wall and lubes the valve seats for better seating. all in all it also increased my MPG's. does give of a little smell out the pipe thats diffrent. nothing harmful. I ran mine all summer on it with 87 oct fuel. and it cleaned up the gunk. i check my cylinder with a flashlight with scope on it. a neat little tool to have. the tops of my pistons cleaned up after three treatments. Also before storing it i got her good and hot and did the deep creep treatment. and fogged the cylinders. witch cleaned up everything after sitting for three months. when i fired her up she smoked for a couple of mins. then cleaned right up. my valves are a little cleaner then yours. but not by much. some stuff is gona stick you cant help that.