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.