this is because you have a carburator made for a 2 stroke, they never work right on a 4 stroke, find a true 4 stroke carb and you will see how consistant they are , you dont need to change jet all the time.. on mine i put a 10+ jet size for the winter and thats all, been running 2 year without adjusment, when its tuned it will always work right
Keihin FCR is the most high tech 4stroke only carburator ever made, developed in the 90s for road race bike for the aftermarket before they went to oem fuel injection, it was later use as a OEM for the MX bike and ATV in the early 2000 and still used in some model, most now also went to fuel injection,
made in small body 32mm OEM Honda CRF150r
Big body, 37-41mm OEM MX bike 250cc and 450cc and ATV 450cc
Sorry for the off topic