gtlotus wrote:UPDATE I installed a return line. It now hold 2.5 psi all the time. I don't really understand why the return line is needed, but it works. Thanks for everyone's help.
Could you tell us exactly which make/model regulator you're using? I'm getting ready to plumb up my system and Holley support was pretty sure no return lines were needed (with 12-804, which looks the same as the discontinued Inglese NG1081 Mark recommends in the Idf tuning guide).