A 77 Cb550 K ought to have PD style carbs from the factory, and have pressed in slow jets.
They are located next to the big cast post in the middle of the carb which contains the main emulsion tube and the main jet at the bottom at the very end.
The slow jet next to it is pressed in and pulls straight out, the reverse of how it was put in during initial assembly.
Padded jaws help to keep from marring the jet itself.
There have been pictures of these posted in this forum. But, I'm too lazy to go search for them.