Is the Amal carb a Premier model?
If so I had a very similar problem with transition of idle to low throttle on a Commando. Took some time to solve. I did the following.
Firstly as suggested take out all jets and check they are correct and clean. One of my jets in the matched pair of carbs was incorrect from new.
Next carefully clean all the internal passages in the carb with carb cleaner and air pressure. The two tiny holes at the back side of the side must be clear and flow when you blow carb cleaner through. This is critical and needs cleaning from both directions.
Next check the fuel level in the bowl is correct. One of mine was several mm different from the other. Amal have a technical sheet on how to do this.
Next check the float has no rough finishes and that the metal tag slots are smooth without metal flash that catches on the float needle. There was a bad lot of floats made so check that. I'll have a look for the post that describes that.
[EMBED content="thread-37631"]https://www.accessnorton.com/NortonCommando/amal-stay-up-float-version-1-and-2-wheres-the-photo.37631/[/EMBED]
Next check the spindle that holds the float is smooth and doesn't jam.
Next check the gasket on the carb bowl doesn't catch the float.
I keep the choke and beleive the bike should be tuned such that it is needed for the first few mins of warm up. As mention make sure it is being operated correctly. Cable tight the choke is off. Cable loose the choke is on.
Follow the detailed Amal instructions for setting the carb.
Check all this about 5 times and in the end you will have it sorted. Be thankful your not using twin carbs.
You can also try increasing idle jet size. Do you have a 17 two ring fitted. You could try a 19 3 ring.
