The problem with this motorcycle is that all of the remedies are all over the place.
No logical thinking.
Like...Try this,no try this... like a squirrel going back and forth all over the road.
Electrical was attacked first. (new plugs)
1. Before ANY work is done with the carb,all other issues must be resolved.
2. Points and condensers should be replaced as a set ,together at the same time.
A volt ohm meter even analog cannot measure how many microfarads the condenser
has or is left to be used.
Lets start from the beginning.
Engines can have these manifestations from being lean and trying to seize up and popping or banging intermittently while idling can be from a bent valve.
I am not saying that is the problem with this bike.
So starting from the bottom: DO NOT SKIP STEPS!
Compression check.
Valve adjustment.
Points adjustment.
Make sure the advancer is not rusted up. Easy to see and test.
Gas tank clean.
Fuel valve will produce a flow of gas.
Check all 4 float bowl drains to make sure fuel is going into each carb.
Just loosen the float bowl screw a little with a rag held under the carb and make sure fuel flows when you loosen the screw.
Make sure all mixture screws are open the same amount.
With the air cleaner off make sure all 4 carbs slides will open when you turn the throttle. Make sure they all start to open at the same time.
Re attach the air filter and start the bike.
Get the motorcycle to idle.
Make sure that it is not popping or back firing while idling.
FACTS: 1978 CB750F
Uni pod filters.
"Bike does have uni pod filters and a straight pipe that has a 1.65' i.d baffle."
This could be the problem because if 4 tubes all dump into one 1.65 inch tube it is very restricted.
He does not say it is a 4 into 1 exhaust.
Floats 14.5mm No mention of this at any time. Previous "mechanic" 
?
Some F models during this time had the accelerator pump and nozzle system.
No mentions of this at any time in this thread.
Stock main jets 105mm (told you they were stingy with this model)
Idle jets #35 stock.
Needle non adjustable. EPA type II
Questions:
Is this a 4 into 1 exhaust or a homebuilt something or other?
Do these carbs have the accelerator pump and nozzle system?
Were the floats set using a measuring device?
Were the float needles replaced at any time?
If they were just "polished" all bets are off.
This is my conclusion: You may not like it.
All of the parts that you have replaced like spark plugs and points and condensers
were a good investment.
The carbs need to come off because there are too many unknowns (float levels) including the previous mechanics abilities.
The float needles if all metal need to be replaced and if they are the metal needles they need to have new seats too.
If they are the rubber tipped needles then just the needles need replacing.
The accelerator pump system if it has it must all be in good working order and squirting fuel.
We need to know what the exhaust system is. A photo or something.
The baffle is ok but the part between the baffle and header pipe is unknown to me.
BTW none of this is your fault.
You inherited these problems because of other people that have worked on the bike.
Like...Too many cooks in one kitchen.
There needs to be consistancy and linear thinking.
A checklist mentality not skipping any steps at all.
One other thing...
If there are two shims on each slide needle it is going to be too rich probably.
You did not say if the shims sit on top of the pocket.
Getting a shim that sits in the pocket but will fit the needle is doubtful.
Some general confusion here.
It would be great to have a photo of those needles.
Measure all of the shims and see if they were deburred and if they al measure the same thickness exactly. Maybe someone just put washers/shims on without checking the thickness.
Trust me - if you go step by step you will run head into something that is messed up.
Never fails.
"So and so told me he thought it was ok" That kind of thing.
