Center six pack with no bowl vent

I just noticed that my customers 69.5 six pack center carb came in the shop with no bowl vent. He had bigger problems so we are building a new motor. I’m assuming that someone changed the center bowl. What would the reprocussions of not having a vent?

Not all Holley two barrel carbs had smog related vents from the fuel bowls, it still has the front vent tube behind the squirters, doesn't it?
I'm wondering if the 1969 six pack carbs had the extra vent tube in them , maybe not

Two on left are A12 auto front, 70 4 spd rear,two on right are both A12 4 spd.I have found quite a few A12 without bowl vent but all were early
March production,all main body casting the same,69/70.Also,most A12 center's had black bowl vent arm.On the Corvette tri-power,the 67 had no bowl vent,68/69 had vent. As to whether it would be an issue,the Holley 4 bbl dual inlet center hung front bowl came with or without a vent depending on the application.

Thanks Bill. All of the 440 carbs I have that are 69/70 have the black rubber bowl vent. Some of the later replacements 440, 71 440 and all my 340 carbs have the vent with the hose. This may be the factory bowl on this carb. It’s an early carb. I forgot the date, but’s its earlier than my oem carb for my A12. It’s has some changes on it. The main bodies have all been milled flat and the metering block has been changed. It does have the 225 plates with the holes drilled in them like we talked about.

I'm pretty ignorant about 6-BBL/Six-Pak/6-Pack setups, but I'm wondering if bowl venting was subject to CA emissions rules ?

I'm sure the EPA was involved on the fuel vapor return systems put into production cars starting in 1970, maybe in CA only but maybe not also

CAP was mandatory in CA in 1966 with 66 Hemi exempt. 67 all motors were CAP in CA. 68 CAP was standard all 50 states. Hence no CAP non CAP list for the 68 and beyond.

They changed to the controlled venting into a hose sometime in 70 but they were only connected on the CA emmision cars. My AAR has it and it uses a three nipple breather.

for 1970:
all the T/A & AAR Six Pack center carburetors are 50 state with a bowl vent

the CA emission (N95) 440 Six Pack center carburetors have a bowl vent (w/3 nipple valve cover breather)
the 49 state 440 Six Pack center carburetor DOES NOT have a bowl vent (w/1 nipple valve cover breather)

for decades the only 440+6 center carburetors available new have been the CA emission units with a bowl vent

for 1969:
all the A12 Six Pack center carburetors are 50 state WITHOUT a bowl vent

for decades the only 440+6 center carburetors available new have been the CA emission units with a bowl vent

Then tell me why the set of A12 carbs I just unpacked,center 4392,dated 121 9,original carbs ,never touched since new,never been apart has bowl vent with black vent arm.


I have been doing carbs since the late 80 s, I have received both sets in pieces and those that were untouched from new,like I said above (I have found quite a few A12 without bowl vent but all were early March production) .

What is the purpose of venting the carb bowl?

I think what Dan is referring to is the WITHOUT bowl vent in his statement does not have the tube. It has the black rubber and arm in the picture. My original question was about a carb with NO HOLE OR ARM AT ALL. What you are saying, Bill, makes sense. I’ve never seen one with no hole so this must be an early set. You answered my question.

my bad, I was referring to this "bowl vent"

the center carburetor on my December '69 built 440+6 Sport Fury GT did not have the flapper vent on it IIRC all 3 carburetors were dated in November '69

That's odd, the middle bowl looks like a different color and the arm to actuate the vent lever is present??

Joe

I saw that lever also (the carb looks a little darker from fuel staining), the float screw/nut looks different as well - but saw no flapper & figured I'd add the pics (taken pre-'90)

The rear carb I pictured has the correct screw,the front is what you get now.Also,the picture of the restored engine has the wrong choke pull off,the straight nipple is 4bbl which is what you get no,the original has a 45 degree angle.

Here’s my November built Superbird carb. It has the rubber vent cover. Bill has already restored this one so it looks a little better. 😬 it’s 226 of 69

No expert on Holley, but are we confusing types emission systems and types of vents too? CAP later CAS was the actual emission control of the exhaust. All States were CAS by 68. The Carbs both Carter and Holley that had a vent tube were for the ECS (Evaporative Control System) which was a requirement for CA only starting in 70. This was capturing vapors, both at carb, and fuel tank to burn in engine or return to tank as liquid. Having a bowl vent with rubber stop (normally open) was not part of ECS since it vented to atmosphere.

Frankly, I do not know why there was a bowl vent to atmosphere that started in 67 for CA CAP/CAS. The bowl vents started showing up on Carter AFB in 67 for the CAP/CAS CA only cars. Became standard for AVS in 68 since all states were CAS. But this was only a Chrysler thing as best I can tell. Plenty of other manufacturers using Carter did not use it despite having to meet all 50 state emissions in 68 and up. Later other manufactures used the internal vent lever to the tube that went back to the ECS.

Having a vent that captured vapors and routed back to tank, or burned through engine makes sense. The vent that went to atmosphere on a bowl that had other vents to inside of air cleaner doesn't make much sense to me, unless it was a pressure thing to ensure proper calibration with a dirty filter. Open with closed throttle, and closed when you accelerated to full throttle and got a pump shot. At least that is how carter carbs worked. Again a Chrysler thing mostly.