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.

 

[Geff McCarthy]

I selected the NGK 5 plugs based on advice here! Gap 0.035 on all. But this mis-firing started before I replaced anything.
And no, i took no other photos.

 

[Geff McCarthy]

I did recheck firing order, which is correct. But...will the engine run if ALL the plug wires are 1 plug off in either direction?? Now that I have the plugs out, I shall position #1 at TDC and verify the rotor position.

 

[Geoff 2]

More BS in posts 48 & 49. Plat & Irid plugs cost several times the cost of a standard plug. So ask yourself why would car makers spend extra [ they try to save money ] on these plugs if they were unnecessary??? They use them because they reduce misfires. They do that in two ways: the reqd firing voltage is less & the electrodes are a much harder metal. The harder metal erodes more slowly meaning the plugs do more miles before the gap becomes excessive & misfiring occurs. These plugs will work better on older cars, not worse, because they require less firing voltage. On an older ign system, you can increase the plug gaps to take advantage of this.

In the link below, note what the last [ underlined ] line says....

 

[Geff McCarthy]

From one Geoff to another, Thanks!!!

 

[gtxrt]

when you do research do both sides don't be hard heads. have you heard of speed talk ? have you heard of big Joe Sherman ?

 

[Geoff 2]

I have been a member of Speed Talk for years. Joe Sherman is a smart guy, he uses AFB carbs. There can be many reasons why one spark plug makes more hp [ & more than 5 hp ] than another, such as plug gap, see below.

David R is a smart guy, but when he wrote THAT he must have been having a bad day....or he doesn't understand electrical theory....or both
[1] Why would you use a low melting point metal [ silver ] for a spark plug electrode that is subject to very high temperatures??????????????????? His explanation of a 'fusible link' defies common sense for a number of reasons.
[2] Apparently David has not heard of quench. No, not combustion chamber quench, electrical quench: when a spark is initiated from a metal surface, the surrounding cold-er metal tries to quench or extinguish the spark. It is for THIS reason fine wire electrodes were introduced; the electrode has less VOLUME of metal & less chance of the spark being quenched.
[3] Fine wire electrodes require LESS firing voltage, not more, which is ANOTHER reason they were introduced: larger plug gaps can be used.
[4] The comment 'neither will conduct electricity very well' shows someone with little electrical knowledge. If substance X does not 'conduct electricity' very well it means it has high resistance. The higher the resistance, the less current will get to where it is needed [ plug gap ]. Platinum has about the same resistance as cast iron, & has less resistance than many other metals. When measuring resistance, length & CSA have to be taken into account.....because they affect the resistance. The Plat & Irid elecrodes are merely 'blobs' welded onto the base material & their resistance would be negligible compared to the rest of the resistances that are in SERIES: plug leads, coil sec winding, rotor gap, plug gap.

 

[dmoore]

Hard to argue with them there facts

 

[gtxrt]

I guess if you can out talk someone you're right. maybe you're having a bad day like David R. and big Joe 2 times engine masters winner can't Dyno an engine after doing hundreds of Dyno tests.

 

[Geoff 2]

Nobody is criticising Big Joe. I have great respect for him. I have been working/on modifying ign systems since the mid 60s. You will get fools on forums like this that claim a spark is a spark, &/or that changing spark plugs does nothing, ign is ign. There is a new company on the block in 2025 revamping the Honda design of the late 80s that had a separate mini combustion adjacent to the main chamber with a small connecting passage. The idea was to get a bonfire going in the small chamber & ignite leaner mixtures in the main chamber.

Below is what happened when spark plugs were changed...& nothing else. A large amount of power lost.

 

[Geff McCarthy]

Geoff 2 you increase in respect...and tolerance...with every post!
So: my next step is to take off the valve covers and crank the engine, and look for anomalies in valve movement??? By inspection, or what measurement. I will video the valve train movement, but are there measurements that I might attempt? THANKS again to all MOPAR SAINTS who have attempted to educate this aging, gearhead , "recovering" fighter pilot...

 

[Geoff 2]

Geff.

I would not remove the valve covers yet.
The spark plugs are very sooty, indicating richness. I have some questions that I hope you can answer:
- is there a gas smell when idling?
- is there a 'hotter' cam in the engine?
- when the engine was running ok, what was the idle quality like? Smooth, rough?
- did you take a vac reading at idle?

The plugs in the pic are a '4' heat range [ not 5 ] & is what I would recommend [ & I use these in my engine ]. 4 is hotter than a 5 heat range in NGK.

If you have a spare coil, I would try it.