Just replaced all of the fittings and tubing on my 78, along with a new carb rebuild this thing is alive again...wow... Anyway, I started it up and after about 30 seconds of idling, it started to whistle... I pulled the breather cap out of the valve pan and it stopped...put it back it started.

This vac system is new, the old vac tree was broken and leaking terribly so I made one with stainless tubing and swagelok fittings. Looks great and is really tight.

Why then is it whistling? Too tight?

 

Did you replace the PCV with all the other new stuff?

 

Yes that is the breather cap that supplies vacuum to the block and reduces sludge right? It's new with new vac line.

 

After more research I should have maybe replaced the filler cap with built in filter...that may be clogged.