It rolls over normal but just struggles to restart.
I'll bet you a quarter that your throttles are too far closed, and the transfers are not fueling.
Here is a base idle-tune for your SBM. This is your base idle-tune, and that is all it is. It assumes that your PCV is functioning properly, that the only air your intake is getting is thru the proper channels, that your secondaries are closed up tight but Not sticking, and that you have a street cam of 230 Intake degrees or less.
Remove the carb, hold the throttle closed, flip it over and look. The transfer slot exposure should be;
for a 220 or smaller cam; about square; to very slightly taller than wide.
for a 230/235 cam, visibly taller than wide.
Using the idle speed screw, make it so.
Now, lightly close the mixture screws all the way, then open them up to 2.5 turns. Reinstall the carb.
Fill the carb, then fire it up. Don't touch anything before she is warmed up.
If the idle speed it too fast or too slow,
DO NOT adjust the speed screw!
Instead, add or subtract timing; with the engine running, just reach over to the distributor and crank it, until you like the idle speed, without regard to the actual numbers. The engine DOES NOT CARE about idle-timing; if the AFR is right, it will idle down to ZERO degrees timing. Later, depending on the cam and cylinder pressure, you can try some other settings but right now, leave the timing-lite in the toolbox.
Now, do this; shut the car off with the key, but before it stops running altogether, turn it back on; she should spring back to life; with the engine still running, do it again. Try not smile your ears off.
Next, shut it off, wait 10 minutes then crank it up.
Click, vroom-vroom, is what you are looking for.
If it doesn't start right up, something is wrong.
Go in the house and stare at your wife's BooBs for a few minutes and forget all your troubles.... until tomorrow.
Or until the engine has cooled to below about 100*F
Touch nothing!
Then crank it.
If it fires right up, well we ruled out percolation right, I mean, the float bowl had to be full enough to start without help from the choke right.....
But if it cranks with no hint of firing up,TOUCH NOTHING!
Get out and splash a teaspoon of fresh gas straight down each primary throttle bore, then go crank it, marking time as to how long it takes to begin running.
If it starts right up then dies, the float bowl is likely empty and your job is to figure out why.
If it cranks up and runs , then it just needed some choke. But
If if it cranks and sputters and cranks but won't fire, and for sure you only splashed just ONE teaspoon down each bore, then it is now likely flooded; floor the pedal, and keep it down! lets see what happens. If it clears and fires up, increasing steadily in revs, LIFT! off the gas man, don't blow it up. When the revs get to between 2000 and 3000, lift right off the pedal and let her idle.
If the cold engine idles, on the trims I recommended, then it is now rich enough...... if nothing else.
This is your starting point.
Now go get the timing lite, install and read it, writing the number down together with it's associated rpm. Also record the mixture screw settings, the approximte T-slot exposure, and, if you have a fuel-pressure gauge, record the psi to the nearest 1/4 psi.
Once you get this done, then you got a buncha other work to do.
You'll know you got it right when:
the engine starts right up when cold, or warm, or hot. Click-vroom,vroom; or something real close to that. AND
the shift from P/N to in-gear does not bang overly harshly, AND
You do not experience any off-idle, or tip-in stumble, when driving away.
Those are other issues related to, Transfer-slot exposure underneath the throttles. We'll deal with those if/when they pop-up.
Finally, to be safe, check your powertiming;
if it is more than 38* don't floor the engine at low-rpm (under 3600)
If it is under 25ish degrees expect that engine to be sluggish, until you get the idle-tune finished.
Ideally it will fall into the window of 32 to 36 degrees somewhere between 3200 and 3600, but you'll have to deal with that later.
Ok so, I know what yur thinking, mmmmmm Boobs; pervert, lol.
Happy HotRodding