Botched Edelbrock 1407 rebuild?

[dvw]

yes single pop, 3 psi pressure. I have not measured pump output per time, but verified that it is pumping. Will check reluctor gap! and check new rotor again. Based on advice I shall also measure new plug wire resistance, and do a compression ck. Thanks to all!!!!

The 3 psi isn't great. But low fuel pressure isn't the cause of the backfire. If the squirt from the pump is strong and it idles smooth I'm not sure if it's fuel related. The secondaries can't open to soon in a 1407 as they are controlled by the weighted air door being shut. I'd start with a compression check to verify no leaking valves. Also pull the valve covers to make sure all the valves appear to open close to the same distance. Inspect the valve springs to make sure none are broken. That will get the mecanical possibilities out of the equation.
Doug

 

[chescharger]

Is your firing order correct?