A strange problem for an RB, these rotary valve carbs usually have a single jet which either works or doesn't.
Sounds like low pressure in the metering circuit, either an internal leak or something plugged.
F-250 5.4 V8 stand. cab, tandem trailer
Ferris IS3100Z 61" L Kaw, Hydrocut 36" 13hp Kaw
Shindaiwa T3410, EB8520 Maruyama HT2300, MS047
Stihl FC85, MS192T, 041AV, MS200