Pattern rules were changed to say the air box to hold the mixture was not allowed, so YS came up with using the valve cover as the box. I like my FZ110. It is worn and I mostly feed it 15%. Needle twiddlers dont like them. A click can be what the difference of good and bad. When you go rich remember you have two strokes of fuel mixture so when the go rich they go rich fast; same with lean. Best is to find a medium point; I only adjust once for summer and once for winter. Keep fingers off if it is running fine. I want one on ignition.
Where does it say that in the Sporting Code for pattern? The only rules pertaining to aircraft are; max 5kg, max 2 meter length, max 2 meter wingspan and max 95db noise level.
You can use whatever engine and airframe you want as long as it fits within these specs.