ahhh, you're doing it wrong. the subframe doesn't have to come off, you will have to get in there with a screwdriver to remove the clamp holding on the air filter, slide the air filter off the carb, up, and turn it to get it out from between the frame and subframe. then you will use an M8 wrench or nutdriver (5/16 also works, same size) to loosen the bolt on the top of the carb, slide the carb back off the intake spigot, and turn that and twist it through the gap. sometimes it helps to pull the carb off so you can get at the top of the carb and remove the 2 screws holding the throttle slide and cable holder in place.
you'll also want to keep the same carb top and cable bendy from your old carb and use them on the new carb, different carb cable bendys have different length and a lot of times the one that comes on the 13:13 is the wrong length for the throttle cable you already have.