Firstly, welcome to ratsun and datsuning. Usually this would be posted in the engine section, but many people will help non the less. There are some nazis here, but we don't tell them that...
If you can provide the year that will help, but if your truck is 75+ it should have the L20B. In that case, unless the jets are totally off, the 32/36 weber should be perfect or even a little weak for your engine. I'm running a 32/36 on my L18 and have never tuned it but still don't have this pop. It sounds like you have an ignition problem to me.
Does your truck still smoke badly since the latest bang? It could have detonated and damaged something internal. If I were you I would check the timing (there is a video on this site about changing a headgasket that will be very helpful for timing). Also, check your plugs, wires, distributor parts (cap, rotor) and all of the electrical connections to your distributor and coil.
I had a loose connection to my coil and had issues of bogging and deceleration on bumpy roads. Once we found it it cleared up.