How can you tell if vacuum advance is bad on amc 360?

To determine if the vacuum advance on an AMC 360 is faulty, start by disconnecting the vacuum hose from the distributor and checking for any vacuum leaks or cracks in the hose. Next, use a hand-held vacuum pump to apply vacuum to the advance unit; if the diaphragm holds vacuum and the advance mechanism moves freely, it's likely functioning properly. If the diaphragm leaks or does not hold vacuum, or if there's no movement in the advance, the vacuum advance is likely bad and should be replaced. Additionally, checking for erratic ignition timing under varying engine speeds can also indicate a malfunctioning vacuum advance.