Hi Doug..Screwing the mixture screw right in richens the mixture so that inferrs you are getting additional air from somewhere or the fuel supply is being compromised. The 'base' setting for an Amal pilot screw is 1 1/2 turns out from fully screwed in with 'fine tuning' around that setting for individual engines.
As you have a new carb at least for now you can assume there is nothing wrong with that but have you verified an uninterupted fuel supply and that the base settings and specs of the carb are correct?
Also the following can cause a weakness in the fuel/air mixture that would affect settings, starting and running...
1)Worn/damaged exhaust valve seat.(it won't be the inlet as this is open anyway on the inlet stroke when additional air might be being drawn in)
2)Incorrectly set valve lifter and/or bent exhaust cam follower.
3)Leaking head gasket/distorted gasket faces.(it can leak inwards as well as outwards)
4)Leaking past the timing plug bolt in the cylinder head. (this should have an annealed copper washer under it)
5)Leaking at the carb to cylinder joint (you should have a 1/4 thick [6mm approx]Tufnol insulation washer fitted here with appropriate gaskets)
You must also verify that the ignition timing is ACCURATELY set at 7/16" BTDC fully advanced and that the adv/rtd is functioning correctly.
Also check that both tappet settings are correct.
Ensure you have the correct spark plug grade and that it is gapped to .018". Do not fit a suppressed plug cap....
Also check you have a good strong, blue, spark both with the engine hot and cold..A weak white/yellowish spark in either case indicates magneto failure..
You'd just as well throw the 'easy start' away...you won't need it if the bike is in good order and set up correctly and it doesn't cure anything if it's not....Ian
email (option): ian@wright52.plus.com