How much vacuum at the line to the block for fuel emissions system on '70 - '71?

[Iconic]

This is the first time in a very long time where I need to sort out an issue.
How much vacuum is at the line to the block for the fuel emissions system on '70 - '71?
Should it be as high as the manifold vacuum?
I am tracing down an issue and disconnected this tube running from the evaporative canister in the trunk up to the engine block. I expected the idle to go up (or at least change a little) when I opened that line. It did not and I can only feel the very slightest amount of vacuum. Should it be as strong as manifold vacuum at idle???
Please help !!
If it is supposed to be manifold vacuum, then i found my issue and that line must be blocked, kinked, or some issue with it.

[Shvegel]

Little to no vacuum.  It is connected to the crankcase and not the intake manifold. In there usual clever fashion they realized if they used manifold vacuum and something went wrong they could suck fuel from the tank into the intake and possibly destroy the engine. Connecting it to the crankcase allows the vapors a path to be burned without running the risk of harming the engine.

[Iconic]

Shvegel,
Thanks for your help. Hmmmmm, yes, that makes perfect sense.
I can feel the slightist amount of vacuum, so I guess I'm ok there.
Back to investigation of the woooosh when I open my gas cap.

[Nicolas Aristodemou]

I had the the same issue with fuel vapors rushing out of fuel filler cap when refilling with petrol. I did several things: disconnected all small bore vent pipes from fuel tank and evaporative tank (emissions type) and blew them clean with compressed air and also cleaned with a guitar string the short steel vent pipes attached to the fuel tank. Then I found out that one of the plastic pipes at the base of the evap. tank had a leak, I cut it and inserted in it at both ends a short thin brass tube to repair the leak. Finally I blew air into the vapor  pipe leading to the engine and checked that it was clean. Upon doing all these I got rid of the problem together with the associate low speed hesitation.

[TJMart]

Is there a special tool to remove the plastic lines that connect to the emissions tank in the trunk? Are they even removable?

[Nicolas Aristodemou]

Is there a special tool to remove the plastic lines that connect to the emissions tank in the trunk? Are they even removable?


I wouldn’t think there is a special tool for removing them, but not sure 100%. In my case I made a clean cut at the leak point with a Stanley knife and sleeved the the two cut ends with a small bore metallic tube.

[Shvegel]

The lines are not removable at the tank.  they are melted to the tank.

[Chris Long]

This is what I used to repair a break in lines.
https://www.amazon.com/gp/aw/d/B07KLYB43N?psc=1&ref=ppx_pop_mob_b_asin_title