To me it sounds like the throttle trim on the radio isn't set right and your idle stop screw isn't set right either.

First thing I would try is reducing the throttle trim on the radio which should close the carb a little bit. Do this until you get a good idle. After that is set adjust the idlo stop screw until it start bringing up the idle. As soon as it starts bringing up the idle back it off a bit. Now hit the brake and make sure the motor keeps running. The idle stop screw keeps the carb from closing when you hit the brake. If it isn't adjusted properly, when you hit the brake you will close the carb, shutting the engine off.

If you can't get the proper idle by adjusting the throttle trim on the radio you might have to adjust your throttle link length.