help using digital tachometer to adjust my 40 hp

[a2012fatboy]

Hi so i decided to buy a digital tiny tach to help me adjust my carburetor slow and high speed lean knobs i'm at a loss dont know anything about motors can anyone please point me on the right direction i would greatly appreciate it i have a 1971 40 hp evinrude m/n 40153 s/n jo2554

 

[a2012fatboy]

oh btw on the motor it has a tag that says 4000-5000 rpm if someone could please give me a step by step or has a link of someone doing it would help me out alot thx again