Using cheap digital tach to set mixture on 2 stroke

[rdhj]

got one of those cheap tach/hour counters so i can see what RPM I am at and to adjust the mixture screw. I have it on the right setting..one spark per revolution....running the motor in gear and looking at the tach, the RPM jumps all around, making it impossible to tell if the RPMs are degreasing as you turn the mixture screw...is this how they work or does the motor RPM change this much

 

[GA_Boater]

The inductive wire may be picking up pulses from other cylinders or wiring.

I set the mixture by ear. You can tell when it's time to start turning the other way because the motor starts to sputter or slow down.

 

[tommarvin]

Like above, there will be a number of turns you turn the idle screw out,after slight contact in,for example our Force was one and a half turns out,and that was perfect, I don't have a clue what yours should be.
You could search online for your idle adjustment.turns out.