As the son of a mechanic of 40 yrs, I also for 28 yrs, and 2 sons now mechanics, I inherited what my dad called his secret formula on tuneups. Now I am referring to old Carb engines of the past and those that may be still running today. What he taught me in the 50’s, I use a little different as to application today. Get a empty plastic oil bottle. Take the cap and put a small nail hole from the inside out in it. Using the oz marker on the side, fill with 2-3 oz of GASOLINE and add equal amount of WATER. (SHAKE THIS MIXTURE LIGHTLY). (you need to mark on the bottle with a felt marker (G/W) for gas/water). Start the engine and with the air cleaner off, rev engine and pour/trickle slowly into Carb throat. You should notice a smoothier running engine as this mixture will loosen carbon build up on the piston crown and improve flame flow. I always flood the engine to die 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. There are probably others who have tried this TRICK.
