I recently acquired my first Fox engine , a 25 BB R/C, at a swap meet .The engine has no markings to indicate that it is a Fox, nor any stamping on the mounting lugs to indicate capacity. It has the tilt-up muffler and MK-X carb. I ran the engine on the bench with an APC 10X4 on Cool Power 15%. Full throttle gave me 7900 rpm and 5400 rpm on idle. The figures recorded seemed way off. I have attached some images of the engine and the exhaust port. Other than the larger prop and synthetic fuel ,which was what I had on hand, any suggestions on what was causing the skewed results?
Compression is strong, plug is an OS #8, HS needle was adjusted for max rpm , LS needle was adjusted for smooth transition and lowest steady rpm. Engine run was messy with fuel/oil spitting from the muffler and front bearing areas. Surprisingly, the engine running without muffler seemed quieter than some of the diesels I run. I took a picture of the exhaust port as I am intrigued by the size of the exhaust opening in the liner. It seems too small and restricted and wondering if the position of the liner is incorrect. In my Google search, I have not come across a picture of the exhaust port for the Fox 25 BB so am not sure what it should look like.
Any help would be most appreciated.