If you have the brown carb rotator block on it you may have set the throttle plate to open the wrong way..Common problem with all the Zenoah engines with the brown block... Horizon should put a better description in the instructions....With the carb on the engine look in the carb, if you see the head of the phillps screw holding the throttle plate on it's wrong.Take the nylon arm off, turn the shaft the right way, and re install the throttle arm...You WILL see the screw head of the choke plate when the choke is closed...Be sure the pulse hole in the brown block lines up with the pulse hole in the carb body...It's the one nearest the back cover held on by a screw in the middle...