I've had that thing in my ride for nearly 20 years and have messed with it hundreds of times
you can use vac advance for better mileage but NOT to correct for a better idle timing. Meaning, some guys use the manifold vacuum to increase their idle timing. The 8981 screws up if you do that so just use vacuum advance on manifold but have it only come in off idle under load as intended
It will work with weights but it's not the best way. Locking out the advance at total (36-38 etc) will give perfect results always. I used it with weights fir a few years and had mixed timing because the computer is limited by what the weights allow it to do
works like this: you have 3 dials, idle timing, rpm to begin advancing, slope
the computer dials use your locked out timing as a maximum setting. 36' locked means it knows it can only give you 36' advance. If you adjust the idle dial to say 16'.....the computer drops 20' from 36 total.
If you use weights and the computer together: let's say the weights are partially out to 30' advance. The computer still wants to deduct 20' from whatever the total is so you now only have 10' idle timing. Only when you are at WOT will the computer give you precise timing
I have it locked 38' for my 383 stroker with aluminum heads. 28' idle setting gives me a nice rpm in gear. The computer gives 20' starting retard so starts are easy.
My only F-up was that my rotor phasing was way way off and I had hard starts when hot. People on this board pointed me in the right direction
it works with all msd boxes I think. It basically goes in series with existing msd wiring like a switch. Easy hookup, a few wires not including the high speed rpm retard option for boost