Thanks JPC_Aero, The J-aircraft link was very helpful. I wonder if putting Bosch 601 injectors into the Ha-40 will improve operation? Or even if they will fit. I have some DB601 sparkplugs, I’ll try fitting them to the Ha-40 first and see if it’s achievable. Jerry Yagen has a Ki-61 close to completion at Precision Aero Productions in Australia. He has a reasonably good Ha-40 for it, but they are having difficulty finding needed parts. Given the DB601 is more common, with some parts availability, perhaps re-engining it with a DB601 would make more sense