Its me again lol

Did the 20* test improve or lessen the hesitation?
Sometimes the fix will be a combination of two or more things, such as more timing + more fuel.

But, yes, remove the carb to check where the T slots are. Here is a trick to check the T slot position without removing the carb every time:
- adjust idle screw so that 0.020" slot is showing. Note where the slot on the screw head is and measure with a caliper from the screw head to the screw mounting boss.
- repeat procedure with 0.060" slot showing.
- record the measurements
- 020-060 are your limits, with 020 preferred. Having it at 020 allows more sweep of the T slot for transition to the main cct.
- people are harping on about centri curves, springs. Forget about that. You have a low speed, off idle problem.
- the 1406 carb has leaner jetting than the 1405. I would rejet to the 1405 specs.
- to determine optimum idle timing is very simple: engine idling, in gear if auto, slowly turn dist to advance timing until you have the highest rpm, by sound & feel. Idle will also be smoother. Toggle dist to make sure the rpm is at max. Now check the timing. If, as an example, it is 28*, you can use vac adv connected to manifold vacuum to achieve this. This is covered in the Edel instruction book. Use an adj VA unit. Using the 28* example, you could use 12* + 16* added with MVA. You will need to fabricate a stop for the VA plunger to limit to 16*. It is all about tuning the combo!!
- once you have idle timing sorted, if too much T slot is still exposed at idle you then need to drill a small 3/32" hole in each pri t/blade & re-test idle speed/T slot position. Keep enlarging the holes in 1/64" increments until the T slot position is correct.
- with T slot & idle timing correct, check for the flat spot. 1405 jetting might correct the problem if it is still there
- once the idle/hesitation is fixed, then you can modify the centri curve & dial in the total timing at WOT. VA goes to zero @ WOT so it is out of the picture.
- report back.