Winter has come and now that its hit sub 40°F my car will vigorously shake for 15-20 seconds on cold starts until it balances itself out. its fairly consistent in doing so but it doesnt feel like it should be. I also noticed it has got some really sooty black smoke coming out the first 10 seconds or so before whiting out.
So for some context, its got 94k on it and ive replaced the plugs, wires, cap & rotor (with oem) in the past 6k miles so, im at a loss and not quite sure whats going on.
Also wasnt sure about the plethora of google results because most of them had newer (non-carb) vehicles so ive come to you fellas.

Am I looking at a vacuum leak?

thanks guys

 

Assuming everything is stock.

Just a stab at it here, but if it only does it on cold start, check the primary choke pulloff on the front passenger side of the carb to see if it operates and holds vacuum. When cold, take the air cleaner off and plug the vacuum hose. Have someone pump the carb to set the choke (should go all the way closed) and start car normally while you watch the primary pull off pod. If it moves it should pull in and the choke flap should open about 1/8" or so on fast idle. If it doesn't move and keeps the choke closed, this MIGHT be an issue until the heat builds up on the choke spring. If it does move but the choke flap doesn't move and stays all the way shut, you'll have to adjust the choke pull off screw which is conveniently mounted on the primary choke pulloff. You cannot adjust the choke spring as the factory rivets the choke cover in place along with a locater tang to line it up. One setting.

If you have a vacuum pump, you can check the pod anytime by simply pulling off the hose going to the pod and hooking the vacuum pump to it and checking to see if the pod pulls the rod in and holds it there.

You can pick up a primary choke pull off at nearly any of the parts stores for 20 bucks or less. A couple of screws on the side of the carb and you can swap it out in a few minutes. Obviously no need to replace if it's working. It either holds vacuum or it doesn't.

To adjust the choke flap opening for a cold start, obviously it's easiest and best if the car needs to be all the way cold, pump the carb once to set choke closed, DON'T START THE CAR. Use a vacuum pump to actuate the choke pull off pod all the way, then adjust screw until the flap is open approx. 1/8" or so. When you have it where you want it, release vacuum, hook up the hose back to it, pop the air cleaner on and start it up and see. It should get you very close. Trial and error.

Looks something like this:

 

What is the sequence of events that you take to start the car? You should pump the gas pedal once or twice to set the choke and give an initial fuel shot, turn the key, and it should start on high idle with the choke blade open about 1/8 of an inch.

When was the last time the plugs were changed?

 

Follow the starting procedure recommended by oldcutlass, if no success it is very likely the choke pulloff leaking or out-of-adjustment as stated by 69HO43.

 

Times 4 on the choke pull off. It may need to be adjusted to open more. Take off the hose, hold your finger over hole, push in the pulloff. If it comes right back when you release the diaphragm, it has a leak and needs replacement.

 

thanks for the responses guys! it was a leak in choke pulloff and ive got a new one on its way.