McCullough 740 chainsaw problem

I don't know how much tweaking you have tried on the carb or exactly what carb you have but if it still runs on full throttle but fails to idle then could you  do  the following and post the result:
Screw in both the H and L screws until they lightly bottom out and  count how many full turns and parts of a turn  in Quarters?
smud6ie

Try This its easier than me eplaining
smud6ie

Sounds exactly like my Stihl. It demands constant babying to keep it idling 

What model stihl do you have?
smud6ie