[RENEW1]

Holly carbs can fail in many ways. Over the years I have had many of them.A high float level along with throttle plates open enough to handle the xtra fuel can result in high RPM. A leaking power valve can also result in high RPM. These conditions can only happen if you have set the idle speed fairly high when the engine was set up. generally these failures result in flooding and low RPM. Sometimes if the carb is set very rich at idle, a vacuum leak anywhere below the carb will add enough air to the fuel to cause high RPM.