Won't start

Loctite № 542 or 592. See here and here.

If you need a new air cleaner thermo sensor because yours doesn't work, send me a PM; I have some new ones.

Rough running when cold: choke problems. Show us another photo, this time of the choke thermostat and pushrod (with air cleaner removed). Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download, and there's a choke adjustment article here; you may well wind up needing replacement parts such as a new choke pull-off and/or put in one of the Electric choke kits.