it has CDI ignition. The CDI box outputs a pulse to the ignition coil.
Yes, CDI stands for Capacitive Discharge Ignition and it works by charging a cap and then discharging it into the ignition coil when ignition should occur.
The most important pro with CDI is that the very short rise time gives a high voltage and due to the short rise time, the air (and grime) around the ignition cables is less prone to ionize (which is the prelude to discharges in wrong places).
The major con, on the other hand, is that the ignition pulses are very short, so they demand a better air/fuel mixture and better timing (than regular inductive ignition) to ignite the gas fully in this short time.
That same pulse goes to the frequency to voltage converter on the tach.
i remember reading that this pulse is around 20kv and the ignition coil boosts it up to 200kv. more reading last night about cdi said the pulse is only 60-100v
Your ignition system can't handle 200kV, but I think it should get higher than 20kV, as this can be accomplished on a simple Kettering (contact) ignition with a so called "sports coil".
I have been up to 30..35kV with an ignition transformer (which is way efficient than a coil, due to the closed field).
But I haven't really done that much work with factory made CDIs, so I wouldn't know if they're coiled down, relative to other types of ignition.
The thing is that I know what wire the stock tach uses, but i have no idea how much power is going through it and dont want to burn my chip
You could make a voltage divider for measuring, that's what I do when I want to measure an ignition system.
GND o--[10k]--+--[10M]--[10M]--[10M]--[10M]--[10M]--[10M]--[10M]--[10M]--[10M]--[10M]--o HT
Put the resistors in a plastic tube and fill it with epoxy when the terminals have been made, then you have an HT probe that'll last quite a while.
For the project at hand, you need a voltage divider which isn't quite that extreme. Whether it's resistive or capacitive won't matter. Find the voltage level at your system and just make a simple voltage divider with resistors and then feed it through a limiting circuit (resistance and diodes towards B+ and Gnd).