Engine Start... What is normal?

[AlexFIA]

I've read a few of the posts on Weber tuning, and I am not trying to repeat what has been covered in the past, but I am new to the 4x2 Webers on V8s (I've had some experience with multiple SUs on Datsuns) and recently started my motor and took it for a few short test drives and wanted to find out what is normal, and what can be adjusted. I wanted to get the "expert" opinions before I started messing with the carbs.

Here is what I have:
ERA 289FIA
Engine built by T&L (won't go much further there)
347 Stroker, Aluminum heads
44 IDF Carbs set by T&L, will have to look up jetting, etc
T&L custom roller cam, with what seems like lots of overlap
ERA headers with side pipes
Four K&N style air cleaners
12° advance at 950 RPM

Cam info is as follows:
Intake Exhaust
Duration @ .050 224 230
Lobe Separation 108
Gross Valve Lift 0.558 0.513


Here are my issues:
Backfiring out of the carbs intermittently on initial throttle opening (not all the time)
Afterfire out of the pipe on deccel (sounds more like: gurble, gurble, pop, gurble)
When the vehicle is static and I run up RPMs to 2500-3000 I get some afterfire from the pipes. I was running this RPM to check the mechanical advance of the distributor. Since I am still waiting for plates, I haven't been able to make any real runs on the street without risking a ticket (I have kept it at low RPMs driving around the block with the exception of very short bursts of acceleration).
When I was checking the total advance, the timing seemed to fluctuate by 1° every time I would get a pop out of the exhaust. Total advance at high RPM is about 34°.
I shut it down at the high RPM setting and pulled the plugs and they looked normal. I am now using NGK BKR7E plugs. Initially I had Autolite 3933 plugs which are much colder plugs. Prior to getting the car on the road I obviously started the engine a few times and ran it, setting the carb balance, checking various parts of the engine, fuel, cooling, setup, etc. After all this, the plugs were fairly black (dry), but then again most of the engine operation up to this point was at idle.

So the question is, what is normal with the Webers and IR manifold? How concerned should I be with the afterfire, and the occasional backfiring out of the carbs? It really does not bother me since overall, the engine pulls very strong, although with very slight hickups at 2000 RPM on acceleration. It starts easily, even when cold, and idles smooth after only a few seconds. T&L made a big deal about the carbs being "set" and to not mess with them, so I am trying to track down everything else before messing with the carbs. Of note however, is that when I checked the carb balance, I did find one carb to be slightly out from the rest. I did use a Permatex header gasket sealant along with the header gasket, I have torqued the header bolts after every time I run the motor, and I used Acouti-seal sealant at the connection from the header pipe to the collector. Any thoughts?