The most likely cause is a mismatch in the range of motion between the throttle lever on the trans and the cable. To check, disconnect the cable at the trans throttle lever and then carefully measure the total movement to go from front to back (no throttle pressure to full throttle pressure). Then measure to total movement at the attaching point on the carb. They must be equal. If not they do sell adapters for the carb linkage, or you can find a different throttle lever for the trans, or you can do some fab and redrilling of mounting holes. Once the total movement is matched, adjust it so the there is no throttle pressure (movement at idle) but it should immediately start to move the linkage as soon as you start to open the throttle. Get this correct or you will cause damage to your trans.