Get your idle-tune worked out first, and then the cold-running on the choke will be a whole bunch easier.
Before you start:
If you have installed a Single-plain intake with a large plenum, swap it out for a hi-velocity DUAL-plain. You can make the engine idle on that hi-rpm intake, with a good tune; but that tune will only be good for idling.
Make sure the gas is fresh, and pours out clear as water.
Make sure the secondaries are closed up tight but not sticking.
Make absolutely sure that ALL the air that the engine is getting, is coming in past the throttles and, from the PCV.
During the tuning, if you have powerbrakes, pinch off the booster supply-line. Later, after the tune is in, make sure it runs exactly the same after the booster is back on line, especially as the pedal is applied.
Make certain the VA is on the sparkport, and that the unit works.
if you have a 1406 AFB style carb, they are tuned pretty lean, yur very likely gonna have to get a strip-kit.
If you have moved the A-pump rod between the three holes, you may have lifted it too high; the fuel MUST exit the nozzles, immediately upon throttle-opening.
Do not set the WET fuel-level too low, as the engine will struggle to get the transfers to wake up
Ok this is a good time to mention;
Your engine has several timing requirements. In order of importance they are;
Power-timing at WOT
Timing at stall-rpm
Part-throttle Timing with the VA doing it's thing
Cruise-timing with the VA maxed out
Idle-timing, with the T-slot synced to the Idle screws.
You CANNOT optimize the Idle timing and still drive the beast without detonation, with the factory systems, so don't even try. AT BEST, with a single-pattern timing curve, the idle-timing will have to be, whatever you get after connecting the markers of Power timing and stall-timing. If you need a different Idle-timing from the fall-out, the you will need a kink in your timing curve, which will require two different from eachother, springs. Therefore, where I'm gonna take you, is gonna make your Idle-Timing as perfect as it can ever be, with the parts that you have; BUT, subsequent changes will muck with it, and you may not get perfection back, without modifying the distributor parts.
Ok, to get you started,
Yank the carb off, flip it upside down, make sure the choke is NOT on any fast-idle step. Then;
set the transfer slot exposure under the primary throttle-blades to no less than square. Both of them equal. Probably a little taller than square will be better, then set the mixture screws to 2.5 turns out. After this, DO NOT RESET THE SPEED SCREW.
If it was me, at this point I would verify the Float level is correct. Then;
Warm the engine up. Put the engine up on the fast idle cam, at or near 1800, then twiddle the mixture screws for smoothest rpm. If your mixture screws have to be more than 1/2 turn from 2.5 out, or the engine runs rough no matter where you set them and the secondaries are known to be closed; then the engine is struggling with the transfers. Get that sorted with needles, jets, or IABs. When it likes 2.5, drop the idle back off the fast idle cam, but do not muck with the previously set speed screw. To change the idle-speed, reset the Idle-timing....... by ear, to say 700 on the tach, in N/P.. say 600 in gear. When this is done, verify that the engine still likes 2.5 turns out, at idle.
After you have this slow-speed system dialed-in, check your hi-rpm Timing, without the VA, say around 3600rpm. Keep it to below 35 degrees, maybe a little less, but DO NOT change the idle-timing! from the previously dialed in Idle-tune. This may require modifying the Distributor guts. Until that is done, it may not be safe to open the secondaries.
After this is done, NOW you can tune the choke. But before you do, have a quick peak at the VA. find out how much vacuum it takes to get her started . Then, when on the choke, keep your eye on what the the VA is/or is not doing, as regards to a stable timing. You can't tune the choke if the timing is jumping around.
The combination of fast-idle after the kick-down, and the Choke Pull-off adjustment, will be critical, but the on-choke timing has to be stable.
As for how much choke-timing she gets, the more the better but, don't go crazy looking for more; she'll run on anything that she is, by now, getting.
The electric part of the choke should rotate the choke to "OFF" by about the three minute mark; depending on how close the idle tune is. This is adjustable by rotating the outer housing to change the preload. You only get one shot at this, during every warm-up.
Ok that gets you the Idle-tune, and a safe 35* of Power-timing.
Generally,
your idle-timing will fall into the window of 5 to 15 degrees. This will depend on how the rest of your timings work out, and how perfect you want things to be. Idle timing almost always gets the chit end of the stick, that's just the way it goes.
Oh, I almost forgot
You're batter needs to be top notch and your starter needs to get up to at least 300 rpm. The Dakota mini-starter can do this,
That ancient reduction-gear starter can too, but it sucks the battery down pretty hard.
