XS400 carb suggestions (mikuni bs34)

Hello,
New here and just picked up a "new" 78 xs400. Anyway, the bike starts runs and idles fine once warm. However starting it is the biggest pain ever when cold, and once its started I cant get it to idle well. It is very slow when cold, Id say around 600-700 rpm at best, and you need to crank the thing forever. Using even half choke seems to only flood the engine. As I unerstand if the bike is hot, using the choke should increase engine speed, on my bike even half choke just stalls the motor. I have the haynes manual for the bike but it says that the carbs arent to be tampered with, therefore is rather useless. I know nothing about these carbs, and therefore any help would be appreciated. I am not familiar where all the adjustment screws are and dont want to further make problems for myself. They are mikuni bs34 units.
Thanks.