I have a fairly new B 2.4,have about 30 flights with the needles set rich for break in,I leaned both out a little and then went to a lighter loaded prop(from 20X8 to a 20X6). The engine always had a very rich mid-range which I lived with, but with the 20X6 it started hesitating 3 times/second at high throttle,I tried adjusting the HS needle while at full throttle, it stopped the hesitation,then after going to idle and then back to high,it started hesitating again. After several tries I realized that just touching and holding the HS needle stopped it from hesitating. ( it sounds sort of like waa-waa-waa-waaa-waa)like its revving and the fuel/air supply is being interrupted at a high rate-approx. 2-3 times per second. A couple gasser guys helped me check out a few things like dirt in the screen,the diaphram gaskets,and I flushed out the HS needle port with air & fuel. With no results, I went back to the 20X8 and it ran normally. After more carb cleaning checks and trying the 20X6 again,I then went back to the 20X8 a second time and now it hesitates with that prop???
I run 64:1 with Belray synthetic. The gas guys said they never experienced that problem before,the only suggestion they had was to solder a brass tube to the regulator inlet,attach fuel tubing and route it to the carb opening next to the choke valve. All the above adjustments was without the cowl on.