In my experience, when a good running engine like the OS .40 LA is quitting on you, it's usually the plumbing, not the needle valve. You should check the needle valve first to make sure you're not running too lean, because it's easy to do, but that's probably not the problem. What I do is just start over at the beginning and take out the tank, and replace all the tubing. Use little zip ties at each connection, and make sure the clunk is swinging correctly. Nine times out of 10, the engine that was giving me problems suddenly becomes gold.