Thanks for your thoughts. Yeah, probably only something we would see at idle/low rpm when fuel demand is low. Yeah, when I took apart truck to paint and bed was off, I put on new tanks and single line fuel sending units since PO removed lines and vapor recovery system. Kicking myself a bit for not doing right, back to original when the bed was off. Oh well.
That's in interesting point about gas caps. My understanding is that Stant gas caps for 73 chevy are unidirectional and unseats to allows air into tank only to avoid creating a vacuum. Only 2 options for 73 chevy cap, with our without EES. Here is photo of cap with EES:
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The cap even tells you to be careful due to pressure. This is probably the reason folks drill holes in caps, to vent them. There seems to be a lot of confusion regarding gas caps and vented or non-venting and direction. In any case, that topic is for a different post (probably hundreds of posts about caps).
The other question is about a 3-port canister connected to ported vacuum. I just don't understand how the vacuum control valve helps the situation. The original post discussed connecting 3-port canister to ported vacuum but that this was not the best way to connect and an outside control unit was recommended. A vacuum control valve will be connected to PCV (full manifold) and ported vacuum but not sure how that benefits the purge. Any thoughts?? I probably just need to look up how a vacuum control valve operates. Is it just better to send vapor to manifold instead of ported vacuum?