Thanks for your response. In response to your questions: it idles and starts fine. The chock does work and is required to start it when cold. The plug is heavily coated with soot after running for a period of time. When cleaned or changed, it runs like it is a new engine. When operating, it starts smooth then it will start to miss occasionally then the miss becomes more consistent until it almost stops running. If I pull the plug and change it, it runs well again before a repeat performance of missing. Gas has been changed, fuel and air filters replaced, vacuum lines have been checked and the only thing left is to change out the carb. Thanks again.