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Tonight I'll measure high RPM advance with and without the advance vacuum, for giggles, because while I know that I have good retard vacuum, I never measured the advance vacuum (more debate there, some say there is zero vacuum at high RPM)....
Greg,
The specs for your engine are with both vacuum lines disconnected and plugged. The vacuum advance is a load based system, not rpm based like the mechanical advance. The vacuum advance will distort the timing measurement when you are blipping the throttle at rest by varying amounts each time. However in practice, the engine is under load at high rpm and the advance you want to focus on is solely the mechanical advance. In other words, if you leave the vacuum connected the actual advance under load, when the possibility of detonation exists, will be different. The amount of vacuum at WOT under load is very small, 1 or 2 inches, below the threshold of the vacuum advance, and if you can measure it accurately, it can tell you how restrictive the intake system is and how much can be gained by reducing the restriction. Have you looked at the spark plugs closely since you advanced the timing ?
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Paul
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