Ok, guys, got a new issue for you.
I haven't seen, let alone tuned a carb in probably 10 years, so needless to say I'm a little out of practice.
I have a stock 304 with a stock 2bbl, it does have headers, but no crazy cam that I know of.
What I have going on is, everytime I would accelerate from a stop, (hard or slow) it would hesitate real bad and sometimes die.
Bad accelerator pump, drivers side front corner of the carb.
When you accelerate, this is the ONLY fuel the carb is getting for that acceleration.
You aren't 'Idling' anymore, so the idle mixture screws can't supply enough fuel,
And you don't have enough air flow through the Venturis to pull main jets in yet,
So the Accelerator Pump supplies a big shot of raw fuel to get you moving under load and low RPM.
I pulled the carb off cleaned it up and rebuilt it.
Reinstalled the carb and reconnected all the vacuum lines.
Runs much better, however my problem has now reversed itself.
When I come down from a high idle (to a stop) or when it sits for too long at an idle it sputters and SOMETIMES dies. Runs very well at take off and through the range now.
Thanks again for the advice.
Vacuum leak, idle mixture or float level.
Probably float level.
Do you go back through tuning when you rebuilt?
Set the idle mixture with a vacuum gauge, or at least do the 50 RPM drop the manual recommends?
Make sure your timing is correct at idle, remove and plug the vacuum advance line to the distributor, then check base Initial timing...
Then tune with idle mixture with the vacuum like still plugged.
The idle mixture needs EVEN screw adjustment,
All the way in, back them about 4 turns out EVENLY,
Then adjust in until the RPM drops by about 50 RPM,
Or use a vacuum gauge and screw them in EVENLY until you get the highest STEADY vacuum reading (Engine RPM will drop when you get close).
Once you get the idle mixture set, make a big effort to find vacuum leaks.
They are hard to find until you get the idle mixture set so the RPM will drop or increase when you find a vacuum leak...
Propane is one way to do it, turn a propane torch way up, with the engine running, and look for the idle to go up when you find an intake leak.
Be aware this isn't real effective since the fan is going to be blowing the propane away at a pretty good clip.
Another way to find vacuum leaks is a squirt bottle full of water,
Hose down all the gasket surfaces, plugs, vacuum connectors, where manifold meets heads, ect.
Idle will change when you find a vacuum leak since the water will temporary plug that leak.
You might also check the brake booster if you have power brakes.
A bad booster is a HUGE vacuum leak when the brakes are applied,
So if it seems like the brakes are doing their jobs, taking more pedal effort to get the vehicle stopped, it's probably the diaphragm in the brake booster...
Once you are SURE you don't have vacuum leaks,
Then you are left with float level.
MC 2100 is pretty sensitive about float level,
(Just a question, but did you weigh the float or shake the float when you had it out? That's usually a good way to see if the float is leaking)
When the float rides too low (Low fuel level) when you brake, the fuel sloshes forward in the float bowl,
If you see black smoke when you stop, then it's flooding, since the fuel moving forward out from under the float and the valve is opening,
You usually get a 'Chugging' before the engine dies.
If there is enough fuel in the bowl to keep the float/inlet valve closed,
Then you uncover the Jets and fuel to the idle passages, and you starve for fuel, this often results in a lean misfire condition, and eventually the engine dying if fuel isn't recovered in time.
Too high of float level will flood out the engine when you stop from higher RPMs.