Certainly the engine will not run if the fuel lines get mixed up. Here's a good diagnostic: Start the engine. Hold the plane upright -- pointed straight up into the air. Advance the throttle to full open. Watch the fuel line going into the carburetor. You should NOT see any air bubbles going from the tank into the carb. Also, by pointing straight up, you are testing the needle valve setting. If the needle valve is too lean, the engine may run allright, but when you point it up, it may sag and quit. this is telling you to open the needle valve. But you have already tried that, so I suspect you may have air leak problems. One of the most common problems is getting air leaks in either the fuel line or the carburetor or around the cylinder backplate or head. Sometimes, after a hard landing or crash, the fuel pickup clunk inside the tank gets forced into the front of the tank. this clunk should always remain in the back of the tank.