Your description is a little hard to follow, but I’m sitting here looking at my TT gp42 and I’ll try to help. First, what you describe as a “tube inlet” is in fact what the needle valve screws into, and should not be removed. There is a spring clip on the tube that will not allow the needle valve to screw into the tube unless you hold the end of the spring out a little until the needle valve has started. As you can see, the spring clip bears against the serrated edge of the valve to keep it from moving easily. After the needle valve is started into the hole, carefully screw it in until you feel it bottom out. Back it out two and one half turns which should be a good starting position. Now check the air bleed adjustment. There is a small screw on the same side of the carburetor as the needle valve. There is also a small hole (about 1/16 diameter) on the front of the carburetor that is the bleed hole. Look in the hole and adjust the screw until the end of the screw covers about one half of the hole. This will be a good setting to start with. With these settings, the engine should start and run a little rich.

Since you got the needle valve supplied separate from the engine, there is always the possibility that it is not the correct one. The TT gp42 needle valve is about ¼ inch in diameter overall. It has a sharp pointed end with very fine threads then a larger diameter shoulder with an “O” ring in a grove. There are then two serrated shoulders one to contact the spring clip to prevent the setting changing due to vibration, and the other to turn when making adjustments. This last shoulder has a hole into which an extension may be fitted and a setscrew to retain it. If the needle valve doesn’t look like this, it is the wrong part.

If you have never operated a small glow type aircraft engine before, I strongly suggest that you get some help from an experienced person before proceeding. If you must go it alone, e-mail me and I will send you a copy of the TT gp42 instructions and some pictures of the proper setup.