My son’s new to us 170 won’t run. He was riding it and it was running fine, then it started cutting out. It will start and idle fine, but if you push the throttle, it immediately starts cutting out. I have cleaned the carb, cleaned the air filter, replaced the fuel pump, removed the tank and drained it and cleaned the tank and the pick up. Still no change. It also has a new spark plug. Thank you for any help.