In a twostroke race enige, they use a timing of - low rpm / 36 degrees BTDC and high rpm 15 degrees BTDC.
Normaly into a Chainsaw engine the distance isn't so big, I think - low rpm 35 degrees BTDC and high rpm 28 degrees

If you don't use other batteries high then 4,8 Volt, a regulaor isn't needed.
I put this regulaor into the schematic for those who use 6 Volt batteries.
If the Voltage is to high, 5,5 Volt, you will blowup the pic.
It's also possible to use a 5Volt diode (.....?) and a resistant to reduce the Voltage for the pic.