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?

 

[1KoolBee]

Make sure you put the larger jets in the front ( primaries) and the smaller jets in the rear ( secondary's). I’ve seen more than one avs/AFB rebuild where they were put in backwards. It will run but will stumble, pop etc

 

[Geff McCarthy]

Status report - thanks again to all!
Compression good on this '77 8.2 CR 400 Initally I was not rotating the engine sufficiently to achieve highest value. I was not really looking for slow reduction that would indicate bad rings, but accidentally I left the gauge overnight on 1 of the cylinders, with no bleed down. The motor has about 20,000 miles, no racing. I now note the low reading on #4, which may be mis typing, will check again.
Simple straight bore scope inspection, nothing seen. I will look into a scope with swivel head to look at valves.
The new Plugs have some carbon on them, equal both sides. The photo shows 6/8; I re-installed the very tough #3 and 6 while under the jacked front end.

Plug wire resistance proportional to length
Reluctor gap 0.010-011
New cap and rotor intact
Sender unit was new 1000 miles ago, removed and inspected, no blockage. I cannot recommend this procedure on a winter day in a Model A size urban garage in this 99 year old house...
Incidental failure of fuel gauge, but there was apparently no tank outlet to fuel line ground connection. I ordered one from Classic Ind.
I have not removed the valve covers to look for anomalies in valve motion. I am not sure if I could interpret anyway.
I also have not substituted a coil, will do that once plugs are back in.
Any other next steps besides the valve train observation, and new coil? Can I measure valve travel to check cam lobes indirectly? THANKS AGAIN TO ALL!

 

[furious70]

Did you take photos of the porcelain portion of the spark plugs inside of the ground strap? Were they all carboned/fouled like that?

 

[gtxrt]

what is the gap on the plugs it looks more than .035. I would go back to the stock type plug and not the needle tip that has been known to cause problems.

 

[Geoff 2]

Rubbish! The 'needle tips' are fine wire electrodes, typically Platinum or Iridium. They require less firing voltage than conventional plugs & are more likely to provide a spark when others do not.

 

[gtxrt]

Rubbish! The 'needle tips' are fine wire electrodes, typically Platinum or Iridium. They require less firing voltage than conventional plugs & are more likely to provide a spark when others do not.

they have problems with a stock ignition system on older cars. plus heat ranges could be tricky on those plugs. again what is the plug gap we see in the photo.

 

[gtxrt]

Rubbish!

strong word for not doing any homework on the subject. it would be a cheap try putting in an older type plug with the right heat range with a .035 gap.