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It's a vent, don't plug it.

You could leave it open if you want, most people don't have problems with that. It would be slightly safer to route it to the breather though, which would mean getting a 2 nipple breather or "T" ing into the breather hose. Read a story in an old mopar mag about a housefly going up the fuel vent and getting stuck between the needle and seat causing fuel to overflow everything and start a fire which burned the car down! What a horrible chain of events.

Tav

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Plugging off that nipple defeats the intended purpose of that vent valve. With that said pretty much all completion series carbs don’t have a need nor have this additional bowl vent valve. For street applications going back many years, carburetors have had bowl vent valves. It is not intended to be the primary bowl vent, it is there to allow evaporating fuel to exit the bowl rather than collect in the air cleaner under hot at rest conditions, which would help to induce hard hot starts. Pre 71’ OEM Holley’s had a simple rubber plug that closed off a hole in the top of the bowl when throttle position was off idle. In the case of six-pack, with the addition of the outboard bowls venting directly into the air cleaner, this single bowl vent valve on the center carb isn’t enough to prevent hard hot starting. Try starting your hot six-pack without the cleaner in place sometime after a good 20min. heat soak.

The enclosed design with the hose nipple started in 70’ with California cars in an effort to collect these evaporative gases and store them in the crank case for later consumption (hose to breather in 70 &71’). Later years had this nipple connected to the charcoal canister.

The stuck needle and seat scenario that keeps coming up with this topic doesn’t make a whole lot of sense to me. A well maintained carburetor/fuel system rarely suffers from such a failure. Even without an open bowl vent valve, fuel will overflow the venturies and primary vent to flood the intake and will spill around the throttle shafts on to the manifold.

Holley technical support will tell you to leave this nipple open for a street application.

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but you claimed that you need that open to vent the bowl and thats not true because there is another vent that is built in and the bowl and that WILL vent with that port plugged. and that was my point.

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but you claimed that you need that open to vent the bowl and thats not true because there is another vent that is built in and the bowl and that WILL vent with that port plugged. and that was my point.

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I think I if you read both of my posts above again, I never claimed the bowl vent valve hose nipple to be the primary fuel bowl vent and should be left un-plugged for that reason. As you have stated, the primary bowl vent is cast through the air horn. My point was/is if you are not running an evaporative recovery system of some kind, it is intended by design that that nipple is to be vented to the atmosphere as was the pre-71’ “rubber plug over a hole” bowl vent valve.

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If you look at the Chevrolet Corvette Holley Tri-Power carb,the only vent is the one cast in the bowl.1970/71 emission standards required it to vent bowl vapor into the canister instead of the atmosphere.It is not needed.If it weren't for California,we probably still wouldn't have one.

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I did not mention in my original post this is a 70 challenger so the breather is correct. The carb is 71 style. When you buy these carbs new thats what you get. Thats why I am asking how it would be routed with these parts. Can I just plug the middle carb top breather?

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If your not going to change the breather to a 2 or 3 nipple unit, PLUG the center carb, it's just an emission vent, it will not reduce, or hamper the function or performance of the carb, leaving it to vent open, is asking for a future mess of fuel on the engine, and/or flame job!, and I'm not talking custom paint either

I've been running/tuning/building sixpacks for about 30 years now, I've seen/done just about everything with them.......

Mike