I have been running a 3w-60k for 5 years now and it is a great engine .
getting it tweeked to run good in the mid range was a challenge
I installed the recommended diaghram vent mods. and also installed a velocity stack and this helped alot.
The remainder of the problem was cured by using amsoil 100:1 oil mix and fine tuning of the carb ..
you may have to run it a little leaner on top end than usual and tune out the mid range gurgle /poping with the low needle . this will cause the
engine to hesitate slightly untill warmed up ,but once warm the throttle response will return to normal and the mid and top end will be clean.

i have been running a 22/12 bolly c/f prop at about 7000 rpms
menz 22/10 7200
3w 22/10 7100
about 15 gals of fuel through it so far, with no problems