Limit total advance???

[Excaliber]

mr0077, he could be seeing the vac gauge "bounce" that might indicate a really high vac reading just for a moment as it settles back to actual HG. He will never see a steady state on the gauge while driving around, shifting gears, on/off throttle pressure. That needle is going to be all over the place, low, high, medium. But I concur, it's possible the gauge is not calibrated correctly, which would only exasperate any tuning procedures.

I mostly use my vacuum gauge for two things I want to know. What is my idle vac reading? I can use that number to determine what size power valve I may want to start with for tuning my carb. It is also a good "base line" for the overall condition of the motor and a general health indicator. I also want to know my cruise speed at normal rpm vacuum reading? That will give me an idea of how much vacuum advance is adding to mechanical advance.

Reading and interpreting a vacuum signal with a gauge is more of an art than a science. To get really good at it you need to see, perhaps over a period of years, different gauges, different engine combo's and different conditions. It's tricky stuff that can easily mislead you to wrong conclusions.