I’m referring to old Carb engines of the past and those that may be still running today, its an “old school” trick, but handy for some people out there. Get an empty plastic oil bottle. Take the cap and put a small nail hole from the inside out. Using the ounce marker on the side, fill it with 2-3 ounces of gasoline and add equal amounts of water. Shake this mixture lightly. Start the engine and with the air cleaner off, rev the engine and pour/trickle slowly into the Carburator throat. You should notice a smoother running engine as this mixture will loosen carbon build up on the piston crown and improve flame flow. I always flood the engine to stall and wait 3-5 min to restart engine. Soaking the carbon helps total results to improve performance. Generally the carb can be adjusted a little leaner and idle lowered. Also you might hear carbon blowing out the tailpipe, which is normal…….i hope, hehe.