Real OS 4 stroke plugs seem to work the best. Generic usually dont work as well for the average person. A real OS plug can solve problems. Full tuning is iterative. Tune high needle then tune low, then tune high then tune low. Tune low in 1/4 turn increments. Besides obtaining a target rpm, when adjusting the needles, especially the high, is how sensitive it is. If you are making adjustments and response seems not responsive, the prop is too big or the engine is not broken in. As an engine breaks in the needles can go leaner. New engine run great out of the box but they still need running to pull the biggest prop. That is why it is best to put it in an airplane and fly a gallon or 2 through it instead of boring 5 min bench runs that you cant wait to stop.