That pop is probably the governor spring. When that happened to me it dropped to idle, no response from the hand throttle, but if you reved it at the carb the governor would fight you. It can be worn through at the hooks from use, or if it sat a lot condensation can cause rust that will eat it through as well (mine broke in the middle from rust through). They still had it at the dealers the last time I looked and you can get to it by pulling the governor case off the front while the radiator is still attached (IIRC, very tight to radiator shroud but it will come off). Too late to look at the moment, but I probably have pictures of the governor case if you need it. Stan.
52 Super M, 53 Super H, 52 Super C, Wheel horse C101, JD 140.