Clean the balancer edge with some CRC Brakleen (red can). You'll find that there are degree marks grooved into it's edge. There should be a pointer on the timing cover, passenger side (i believe, the 289 might be on the drivers side, but you'll see it). Clean it also. Get some liquid paper, and mark the tip of the pointer. Then draw a thin line with liquid paper along the 12 degree line on the balancer. Disconnect and plug the vacuum hose at the distributor. Hook up the timing light. Start the engine, and point the timing light at the pointer. Pull the trigger. The white mark on the balancer and the white mark on the pointer should be lined up. If they aren't, loosen the distributor hold down bolt and turn the distributor until the marks are lined up. Tighten the distributor hold down bolt. While the engine is still running, and with the timing light on, snap the throttle. The white line on the balancer should jump a few inches, and then settle back down in line with the pointer. If it does, the mechanical advance inside the distributor is working. Next, reattach the vacuum line to the distributor. With the timing light on, slowly bring the idle up to 2000 rpm. The timing mark on the balancer should slowly move as the engine speed increases. release the throttle to idle again. The mark should drop again. If it does, then your vacuum advance is working properly. Shut off the engine and make sure the distributor is tight. Go for a test drive, and jump on it hard. If it pings at all, you need to retard the base timing (with the vacuum disconnected) by 2 degrees, and try again. Keep doing this until it no longer pings. That's it.
Take care,
-Chris
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