It's probably a bit rusted inside. I have a way to help keep the line open that we use in old motorcycle petcocks. I did this before I installed a new under bed tank. I got from the hardware store a fine screen-mesh brass cloth and soldered it to the brass tube that fits to the bottom of my tank. I wrapped the screen around a pencil, soldered the seam and one end. The other end fits inside the brass tube, soldered in, then threads into the tank. It's about 1-1/2 - 2'' long and allows plenty of gas to flow. It acts as a pre-filter. My brass tube used to get clogged because there was SO much crud in my tank, like you redgreen, it would not flow gas. Also re-place a large inline filter close to the tank.
