These carbs must be properly rebuilt, and that means CLEAN. The main jet (white arrow) comes out of the center bore (yellow arrow). There are 2 o-rings on it that must be replaced. ENSURE the lower ring is removed. It is easy to miss this, and if not removed, the engine will never run correctly. A hooked paper clip will get it out. Also, the needle seat must be removed, again, with a paper clip. Do not scratch the carb with the clip. The red arrow points to where a welsh plug is located. It has to be removed to get the carb clean. New welsh plugs come with the carb kit. A Q-tip works good to get the hard to reach areas clean. If the carb is very dirty, the body should be soaked in a carb cleaner overnight to get all the small passages clear.