I had a similar problem with one of mine after I flew through a tree. Nothing I tried worked so I broke down and bought the complete needle valve assembly, problem solved. The needle valve got a slight bend in it as the plane smashed it's way to freedom before it crashed into the rocks!! I could have probably just replaced the valve but for the low price I wanted to make sure I fixed the problem.
At that time the engine was in a Decathlon and using a 12X8 APC and when it went into my Tiger Moth it had a 13X6 APC. I only mention the prop at all because it's a combo thing and depends on the plane the engine is used in, I didn't see what plane you were using.