I put 8oz of Marvel Mystery Oil in my fuel tank and only 4oz in my engine oil. The lifters that were clacking went away and the performance "seems" to be better. Next oil change I will replace one quart of oil with one quart of Marvel Mystery Oil. This is recommended by MMO between oil changes. I still have about 3000 miles on this oil change so I may drain off half a quart now and replace it with MMO to clean any sludge and varnish that may have collected during it's 98K miles. Anyone else use Marvel Mystery Oil?