I make up my own on a lathe. I just turn down a diameter to .154" and chase an 8-32 thread on it. That is the most common size. A nipple is turned on the back and drilled about half way through, and then cross drilled about where it meets up with the venturi. I would show you a pic, but my wife run away with the camera for a few days. Another method which is easier if you don't have machines, is to screw in a pressure nipple just above the casting in the venturi. Another regular needle valve can also be used, and just solder up the end with the needle, or set it very rich. Is the XLS .36 a quick motor? My XLS .15 is pretty good, I had been thinking of making a fast combat just for something to try. I have lots of .40's I could use, just wondering.