Author Topic: Blocking off front vent?  (Read 3225 times)

Offline 1983zsled

  • Garage guy
  • **
  • Posts: 18
Blocking off front vent?
« on: April 14, 2016, 01:22:01 PM »
I have just rebuilt a 1708 5586 carb for my .030 over 396 BBC for my 66 Chevelle SS. I have built a few carbs with Cliff's books, parts and guidance. Without getting to long winded, My 66 does not have any canister for the evap off the front of the Carb. OK to plug or no?
I have a mechanical fuel pump, stock lines from the gas tank etc.
I have searched the net and some say yes, others say no, that blocking it will cause issues.
As far as I have read and understand it's sole purpose is a vent, however there are other places the carb vents right?

Thanks.....





Offline carmantx

  • Carb lover
  • ***
  • Posts: 182
  • Quadrajet Power.com
    • Quadrajet Power
Re: Blocking off front vent?
« Reply #1 on: April 14, 2016, 04:00:28 PM »
Think you are fine to block off that vent tube.
'72 Buicks for fun and drag racing
quadrajetpower on facebook

Offline 1983zsled

  • Garage guy
  • **
  • Posts: 18
Re: Blocking off front vent?
« Reply #2 on: April 14, 2016, 07:39:03 PM »
Ya I think so too. Whats the worst thing that can happen? I don't think that there is that much vent demand?

Offline Cliff Ruggles

  • Administrator
  • Qjet Hero
  • *****
  • Posts: 5418
Re: Blocking off front vent?
« Reply #3 on: April 17, 2016, 01:51:47 AM »
Only one vent is needed for the fuel bowl, but most q-jets will have several other places that the bowl will vent, and the POE wells may also have external vents on many models.  The POE vents can be internal, but you must have at least one external vent for the fuel bowl so it can fill when pressurized fuel passes the N/S assembly......Cliff

Offline markedmondson

  • Garage guy
  • **
  • Posts: 21
Re: Blocking off front vent?
« Reply #4 on: May 02, 2016, 07:12:46 PM »
The canister has a vapor hose connected to the car's PCV system.  It also has a vacuum line connection to the front of the Q-Jet used as a signal, not a vent.  If your car does not have a canister, just run the PCV line normally from the carb (it's the port on the front of throttle body, below the fuel inlet) to the PCV valve, and plug the unused vacuum port on the carb.