I put a pressure gauge on mine and watched it drop about 2-2.5 psi after I had clamped down on the return line then open it back up again. The Carters carbs, I've always heard, are a bit sensitive to pressure. After some research here on some older Moparts threads I found that the trick was to restrict the return line as even the factory .060" was a bit fat. Recommended was closer to .030". I soldered the return line tip closed then drilled it to .032" because that was the closest drill bit I had at the time. My pressure drop is now around .5 PSI. Even with the smaller hole it still passes plenty of gas. I rigged up some clear tubing for several weeks but rarely saw any bubbles.