4150, huge stumble and dies in gear.

19 inches in neutral. What is the idle-timing and idle rpm?
19 sounds like a stock or near stock cam.
For a stock long-block 318;
>Be sure the secondaries are closed up tight,and that the PCV system is hooked to the front of the carb,and working, and that the power brake booster is not sucking air.
Then,for the dies going into gear;
>The only circuit that is supposed to be operating at idle, is the slow-speed circuit. This is a combination of fuel level,transfers slots, and mixture screws. I have a feeling your T-port sync is messed up. With a stock teener; I would start with no VA,and 12* of idle timing, and idle speed up to 650/700N, and the mixture screws at 1T out. But with the big throttle valves, I might have to idle at 700 to prevent a tip-in sag.Get the AFR a little richer than 13.8/14, by opening the curb idle. If the rpm goes too high retard the timing.If too slow advance it a tad.
Alternatively,you can zero in on the correct T-port setting by removing the carb and flipping it over and readjusting the curb-idle so that that the transfer-slot exposure is square to a little taller than wide,and the resetting the mixture screws to 3/4 t out. Then bolt it back on.After this do not reset the curb idle screw.Do not reset the curb idle screw. Set the idle speed with idle-timing and idle-air bypass, although there is a great chance that the idle speed will already be too high with the speed screw set this way. This is because of the amount of air sneaking around all those huge airvalves. You may have to clamp the PCV closed to actually reduce idle-air bypass, or else the idle-timing will just become too low. And when the timing gets to zero advance, well you know that is just gonna be soooooo lazy.lol.
You need to get the engine to idle down to under 700, so that the airspeed past the low-speed circuit ports doesn't tank when the TC drags the idle down yet further. In other words you need to deactivate the TC, by slowing it down, allowing it to slip.
Try this, the next time the car is moving; as you come rolling to a stop, put the tranny in neutral, and then back into gear, and accelerate a little. Then repeat;each time coming closer and closer to a stop.Watch the AFr.
But
If the cam is a little bigger (for a teener), the C/R is high, the idle timing is 22, and the rpm is 1000, then 19" starts to sound sorta normal.In this case the 950 s still way too big, and the airspeed drop when going into gear is deadly. And still, you are gonna need a bigger PV,sooner or later, an smaller MJs.
>But you called it a "pansy motor", so Ima thinking she's a stocker, and I can't figure out why you would want to put a 950 on it; the airvalves are just too big. Vacuum starts to drop almost the instant you step on the gas.
Then for the stumble;
Your accelerator pump better be working real good.
Good luck,fella