A: This may be caused by a rip or tear in a base gasket, air horn gasket, or adapter gasket or some foreign material stuck in an air passage of the carburetor. Inspect the gaskets to make sure you have no vacuum leaks of any kind. Check to make sure carburetor is seated correctly, and is fastened with the correct hardware. You can perform a quick check to find external vacuum leaks (such as a leaky carb base gasket) by spraying starting fluid on suspected areas while the engine is idling. If the engine speed changes for a second or two after you spray an area of the carb, you’re found the leak.