You need to remove the aircleaner and take a look down the carb. You will see 2 small brass rods ending in a circle with a very small hole thru them. They should atomize the fuel and spray it down into the carb but because they are so small they often plug up and cause a surging idle or worse no idle at all.This has covered many times but before you go replacing a bunch of parts try using a can of compressed air sold for cleaning computer keyboards,etc and using it to blow out the tiny holes. There was a fix from the factory for this that called for opening up the holes a bit but you will have to search for it since I cannot recall the size. Big Jim has mentioned many times that you can use a small bottle of propane to locate vacuum leaks. For this you start the motor and while staying carefully away from rotating parts open the valve on the prpane a little and release the propane around the carb base, vacuum limes etc. If there is a leak the propane will cause the idle to increase and you will have found your leak. Also do not wear any loose clothing that can get caught in the fan belt, etc. Hope this helps, my friend uses the can of air on his carter bbd and it works great.