Silversurfer, you seem to be pretty knowledgable on the Brisons , i have a new fox 3.2 very similar to the Brisons, however i think i prefer the Brisons, anyway i am having the midrange burbles and engine running ruff at mid throttle also , and i am running Lawnboy 40/1 , i think after looking at my plug after 1 gallon of fuel i am going back to the sythetic Amsoil 2000 mixed at 64/1 . My plug was black with some carbon build up on it, so i think my mixture was to rich. Although i ran my Brison 3.2 yesterday to which is new and it ran fine on the lawnboy mixture with no midrange cutting out and running ruff. It has me stumped right now. Hopefully i can get it solved today.