Front carb pump not working - poping sound at high speed

[boeing7873]

So I started over with all the checks since I did not find any vacuum leak anywhere using the ether technique.
My next check was ignition timing. I had it set to about 7 degrees, using the following technique.
I measured the pulley diameter. the circumference is then 2*Pi*D/2. I divided the circumference by 360, multiplied by 7 and marked the pulley at about 16 mm before the TDC mark. Is this a good technique??
I started playing with the distributor and tried increasing the advance even more than 20 degrees and what I observe is that after about 25 degrees, I can't keep advancing even if I keep turning the distributor.
I noticed a significant improvement by advancing the timing. I estimate that now I have an advance of about 10 to 15. Can't really tell, but the truck runs much better.
Another discovery is that #2 cylinder is running lean, the plug is white. I checked the carb accelerator pump jets, and while the other 3 jets spit a clean flow, #2 is messed up. I will exchange the jets after cleaning them and make sure I am getting the fuel I need on acceleration.
Another observation. The auto advance does not happen until about 1700 RPM. Something wrong? Lubrication? Anything I should do?

Running pertronix - nkg bp6es plugs changed recently - blue Bosch coil
Carburetor rebuilt to the best of my skills and knowledge. New gaskets. Float level checked with the correct tool/technique with engine pump running.
New fuel pump.
New fuel lines. and transparent clean fuel filter.
Tested auto advance with RPM and it looks like it is working fairly well. Back and forth.
Idle screws are to 3 turns out now.
Adjusted all valves and found all exhaust valves to be tight. Now all back to 0.2mm.
I bought starter fluid. Sprayed the base of the carbs and the shaft ends. No noticeable increase in rpm.

[pinzinator]

Perhaps a bad plug wire? Is it possible that 2 plug wires are swapped? Fuel solenoids OK?

[boeing7873]

Running significantly better, I think I have played enough with the timing to get it to where I need to move on to the carbs issues before coming back to timing issues.

The engine now idles quite well but still hesitates stalls on initial acceleration. I started looking at the carbs again after discarding the vacuum leak at the intake manifolds.

The problem is the front carb accelerator pump. For some reason, it is not working as the one in the back carb. It simply requires a much faster stroke to deliver fuel. I changed the rubber seal on the pump again, and I see no changes. Are those check valves at the bottom of the carb the possible issue?
Do they commonly fail?

Exhaust backfiring still occurs and I have detected an exhaust leak between the first segment of the exhaust and the flexible segment, before de muffler. Could this be the cause of backfiring?

Finally, i can hear a popping sound from the engine, possibly from the carbs, as if popcorn was being done deep inside the engine.

Thank you,
Jeronimo

[Buzz]

Yes, they do. To check them you turn the key to the on position. Then unplug the electrical connection from each valve and then tap it back against to terminal. You should hear a clear click as the solenoid clicks open. No click, then the solenoid is probably stuck closed and is cutting off fuel to that barrel of the carb. Weak click could mean partial operation.

[boeing7873]

Yes, they do. To check them you turn the key to the on position. Then unplug the electrical connection from each valve and then tap it back against to terminal. You should hear a clear click as the solenoid clicks open. No click, then the solenoid is probably stuck closed and is cutting off fuel to that barrel of the carb. Weak click could mean partial operation.

Sorry... I did not describe the valves correctly. I was referring to the check valves of the acceleration pump. those are two screw/plug type right under the accelerator pump shaft. If I remember correctly, they have a ball and a spring inside. These are 01-40-49 and 51... they are around $50 each!!!!