Lets start with model type and code from the engine valve cover. Since this engine came in both a single and twin cylinder can make a difference in how we proceed with helping you.
Have you checked to see if the throttle is actually opening when you push the control cable to the high speed position? With the cable moved to this position, try moving the throttle control on the carb moves freely. If you close the throttle control and let go it should pop back to the wide open position. If it doesn’t, you need to adjust the control cable forward, fully opening the throttle. To do this, loosen the cable clamp and push the cable toward the carb til it stops. Then tighten the clamp and test the unit.
There are two parts to the cable. An outer casing and an inner wire. The inner wire may have stopped moving, but the outer casing may need to be adjusted. To adjust the cable, use the steps I listed in post #4. Not uncommon for the outer cable to have moved back, not allowing the control wire to do its job properly.
