Hi Tom and Friends, Need some help. I have been adjusting and rebuilding Walbro Carbs for years. Recently my Trusty "Pop-Off" unit #500-505 would not hold pressure. Walbro does not have a rebuild kit for the unit. A new one from Walbro is listed for over $200. I found a distributor that will sell a new one for $80. All I need is the flapper valve. Does anybody have a solution for me. Thanks, Col Chuck Winter