If you still have issues with fuel mixture at throttle settings below 1/2, remove the barrel from the carb again and use a NEW Xacto blade and get every speck of crud out of those metering grooves. There will be a groove on either side of the feed hole. This must be spotlessly clean. Also, if using muffler pressure, expect to have the airbleed trim a little more open. Stick to starting half way closed or a little more closed from 1/2 and work from there. It’s always ALWAYS better to start rich and work leaner.

I have a 60XF IV Heli carb that I was given - I tried using it on my ST .90, but the midrange was so sloppy rich, no adjustment could clear it up. One instance where a Heli carb isn’t suitable for fixed wing/prop engines.