I've had a 3w60k since they first came out (long ago !!!!). I had difficulty with the mid range burble and tried several things to improve it but it has never completely been resolved . The carb on mine was difficult to find the sweet spot for overall performance . If I leaned the low end enough to
smooth out the mid range it became difficult to start . I also was running the recomended 22/12 prop but found that the mid range improved with a 22/10 prop. I also added a remote vent tube to the diaghram cover and a velocity stack. The timing is at 28 degrees btdc. Having made these changes made it easier to tune and greatly improved the mid range burble ,but is still there around 3400 rpm . I have considered changing the carb but at this point its performance is good enough for me. Has anyone replaced their carb ,what carb did you use and what issues did you resolve ?