From what I've read it seems like the model 5001 is for control line. Even if that's the case, you still need to be able to tune it.
You can check out Enya's website, but I didn't find much info there to be honest.
Hopefully someone without more experience with Enya engines will stop by and offer some more insight into where you may be able to find a needle valve for your engine.
If you have a picture that would probably help too, just send it to matt-brown@hooked-on-rc-airplanes.com and I will post it on this thread.
It also may be helpful to contact Enya directly for information on where to get a needle valve for your engine.