Do you know when you remove your gas cap and you hear that "whoosh" sound? I am pretty sure it is a vacuum that builds up in the tank for emissions purposes... right?

Well, after I put on either my Carter mech pump (with no return line and simply capped the stock return line off) or after I installed a Holley carb and maybe got a vacuum line on wrong, I no longer have that vacuum in the tank. My only concern is if they check for it when I get e-checked next month...

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1984 z28 w/ a 357 cu in. monster engine which is looking like the posterchild for Edelbrock with the exception of the Holley 750vac... all the suspension stuff... 9-bolt posi disk is in...

-=ICON Motorsports=-

 

All tanks are vented in some way.
Basically the pump creates a vacuum by removing gas, and since its technically a sealed system, there is a vacuum since there is nothing to take the place of the fuel. 2 things happen from there. One setup (on the TPI and maybe TBI) is a one way vent that allows air into the tank, but not out. The other is the charcoal canister, it bleeds off and attempts to reuse fuel vapor pressure from the tank and puts that into the engine. There is usually a little pressure in the system, since they dont want all those harmful vapors in the air. Make sure the charcoal can (if its still hooked up) isnt full of gas. Thats about all I can think of.