Gonna assume you have the right throttle cable, with the metal tube on the housing clamping end.
Try this...take the throttle return springs off, with the throttle cable un-hooked, make sure the carb throttle arm will make the full swing.
With the metal end of the throttle cable housing in place, in the clamping bracket, the cable itself free, should be at full throttle (via the gas pedal). Okay. By hand, pull on the throttle cable to check for free movement. If it's good...
Let the cable rest where it is (again, should be full throttle). On the carb throttle arm, hold it at full throttle (WOT), and compare where the cable end is to it. On the cable housing, move it through the clamp, until the cable end is just forward of being able to fit the carb throttle arm. Don't hook-up, yet.
Let the throttle arm go back to idle. Then, by hand, pull the throttle cable forward. You want the cable end position just forward, to fit onto the throttle arm. Just adjust the housing end, in the clamp, until it all works full swing. Once in position, tighten the clamp, and hook up the springs.
