EVAP canister help

[Marteney, Steven J.]

My last two gas station visits have shown that when I remove the gas cap
from my 89 Formula 350, '165 absolutely NO "sucking" sound is made.  It has
done it before but it was only a quick fizz.  Does the tank run under a
vacuum, therefore the sucking sounds when you crack the cap?  Does it take
time for this condition to develop?  (In other words, start car, quick drive
to gas station, shut-off, typically no suck sound?)  Likely a bad gas cap?
Bad vac line?  Bad canister?

I know my 87 T/A 305CCC was quite obnoxious when the gas cap was removed.
I'm wondering if this is the cause of my laxluster gas mileage even BEFORE
the motor was rebuilt.  Any ideas on how to test?

Steve
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