Busy week. Flew one CFI lesson with Sam in 172, upon return carb heat jammed. Now awaiting parts. Flew a mission to DC woth Sam for Faith. Flew a refresher with Mark M. In between I dye tested the three original cylinders and the potential replace,emt "barn" cylinder IAW AD 94-05-05 R1. Also looked at valve guides in the "barn" cylinders. All worn, esp. the one I picked to send out for chroming.