I've had trouble with difficult hot starting (flooding), flat spots on acceleration and miss-firing at/near w.o.t. ever since I bought the 3B. Adding the overdrive made the symptoms more obvious. My carb turned out to a 'Franken-YF', so I ordered a rebuilt one from scoutpilot. The f-head runs like a top now. Very happy. I only had to adjust the idle speed. Was able to accelerate to 60 up a slight grade and hold 55 up one of the steepest grades around here. I drove a couple miles at 65 just to see what it was like.