Chevrolet Repair: Egine knock after replacing EGR valve, damper pulley, vacuum gauge

Question
My son has a 1982 El Camino, 305, 4BBL carb, auto trans & its all stock. The truck has had a rough idle since my Father gave the truck to my son.
It gets poor gas milage, has poor transition from idle and uses oil (a little drip & does not appear to be burning oil)needs about a quart every other tank full of gas.
This weekend we pulled the carb and cleaned it best we could. The bottom of the carb & the intake had lots of carbon build up. Performed a vacuum test on EGR, it failed so we replaced it (it also had alot of carbon build up).
We replaced most of the vacuum lines & checked others for leaks. The engine starts easily and idles well and runs like it gained 20 to 30 HP. The timing was advanced by using a vacuum gauge to the highest vacuum and then back off a couple of pounds. But now we hear a loud knock. It sounds like its deep within the engine (does not sound like a lifter taping or fan belts. I tried using the old listing method using a metal rod but could not find any spots where the volume changes. What would cause knock to appear so sudden?
Thanks,
David  

Answer
Hello David,
I would probably back the timing off just a little and see if that helps.

I would also remove the belts and start it to just see if a belt driven accessory was the cause. While they are off, see if the damper pulley is in good shape and not loose on the crankshaft.

Another place to listen for a knock is back at the torque converter. It could be loose.

Van