Engine in my '72 pulling too much vacuum. PCV Constantly rattling.

[lha1992]

Hi all! So just recently in the last 2months i finally got my first 67-72 truck. A 72 C20 custom camper 2 tone deluxe. (pictures coming soon!) Anyways the truck has a motor from a '76 in it but has been prolly warmed over in the past but is obviously warn down and prolly does need new rings which means blowby.

Well i just recently changed the intake gaskets because the front seals were leaking some coolant and i converted it over to HEI also (hasn't been timed with a timing light yet, only by ear). Anyways, lately that has been weird is that my PCV valve has been constantly rattling and i cant figure out why?

I mean i thought it was a bad PCV valve but i changed it and its still bad! Really what its doing is the engine is pulling sooo much vacuum its sucking the ball from the end of the PCV back up obviously closing it off but not fully because you can put your finger on the end of the PCV while the engine is running and its still pulling suction. I change the vacuum hose because the engine is pulling soooo much vacuum that its even sucking the hose shut as in blocking it off.

I can't figure out why its doing this? Could it be timing? Carb tuning? What? Before the intake gasket change i don't remember it doing this before...Its just weird that even pulling the valve outta the valve cover that its pulling so much vacuum to even be sucking the hose shut.

[68gmsee]

Replace the pcv first. If it still rattles check the vacuum with a gauge to see what the number is. Usually in the 17-22 hg range. Vacuum gauge can also tell you other things about the engine.

Scroll down for description of symptoms.
http://www.gregsengine.com/using-a-vacuum-gauge.html