Adjust the lo mixture for highest RPM'S at idle and hi mixture for highest RPM'S at full throttle. Adjust the idle just until the chain just stops. Repair Clinic and E-Replacement Parts have parts. E Replacement Parts has exploded views and videos.  Morrison Outdoor Equipment has parts and Brigg valve guides and valve guide tools for Brigg lawnmowers. A CJ8 is a little hotter than a CJ7. A J61 is MUCH hotter!