Hello, I am a newbie and have built one motorized bike and enjoyed it much. I am an old retired man getting up in age. I have a problem and hope some one can help me. I have purchased a 49cc made in China engine and have it installed and riden. However the engine runs too fast with throttle closed almost uncontrollable. I have very carefully examined the carb and can find only one adjusting screw.which make no difference while adjusting. Everything I read says there should be a high and low adjusting screw. How can I get the engine slowed down? Thanks for any help.