My Ford 7.5 carburated motor is running rough
Anti backfire isn't built into the valve it is a separate modification available from Holley. Kit consists of a small spring, check ball, plug and drill bit with depth control. You drill the base plate power valve vacuum port and insert the spring check ball and plug and your done. I just did this on my 87 4180 Holley while I was doing a carburetor rebuild.
1988 Fleetwood Limited MH - John Deere Chassis