All Small Six Vented carb bowel swap

[DON]

I am thinking of swapping the fuel bowel on a Holley 2300 with a new one. The problem (?) is the old one has the little button vent on top and the new one is unvented. I know the bowel is still vented through the body, but is there any drawbacks or problems with this swap? Any hacks for putting in a vent?
I worry about what would happen if there was a failure with the needle valve or float and fuel didn’t get shut off?

 

[powerband]

not sure what is a 'button vent'
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AFAIK - 2300's are vented through metering block where meets carb body and up vent into AC, overflow drowns carb ... . Performance use has a simple mod called a "Whistle" that keeps fuel in bowl from sloshing into vent on accel. etc ...

https://www.jegs.com/i/Holley/510/26-89/10002/-1?gad_source=4&gclid=CjwKCAjwtdi_BhACEiwA97y8BBEC8y-eDL_lwkT89UXiFsuTO3JDqwveiLbRa5L_qhpmMIWVTBUhNxoCM5QQAvD_BwE

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check it out:

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2300 mod'd for pressurized fuel bowl - Blow Thru forced induction with 'whistle' at bottom center in first pic
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.... with Maverick/250/2300/Blow-Thru SC, boost inconsistent until pressurized fuel bowl vent in hat was extended into charge tube with tubing @ 6 ".

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have fun
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[DON]

I have the whistle installed. You can see the button behind needle valve.

 

[DON]

You can see the vent button behind the needle valve

 

[DON]

Do you want a better pic?

 

[powerband]

yes, better pic wood b good...
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marine / industrial application bowl ?
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here's Summit's typical variety

Free Shipping on Orders Over $109 at Summit Racing

Find Parts and Accessories holley 2300 fuel bowl KEYWORD and get Free Shipping on Orders Over $109 at Summit Racing!

www.summitracing.com

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( just when I thought I'd seen everything Holley 2 Bbl ... )

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Have Fun

 

[DON]

No, just old automotive.
I guess if nobody is familiar with the vented bowel, no one will know of the drawbacks of swapping out a non-vented.
Just my luck

 

[powerband]

thanks for pics, now I must have seen everything Holley 2Bbl ...
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can't figure why it's there, I'm thinking a 'fuel purge port' rather than 'vent'.
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2300 - 2 X 3 Offy Port/Plenum mod' . ( 500Cfm 4412 )
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[DON]

I call it a vent for lack of what else to call it. I do know gas comes out there if the float gets stuck. I guess that’s what I want to know is where will it come out if the hole is not there?

 

[Frank]

I call it a vent for lack of what else to call it. I do know gas comes out there if the float gets stuck. I guess that’s what I want to know is where will it come out if the hole is not there?

Don there's an advantage and disadvantage to externally vented bowls:
Major advantage, it reduces hot soak vapor flooding. The hot carb will vent the evaporating gas form the top of the bowl before it climbs the internal tube and vents down into the intake. This makes cranking time less on a hot engine restart. The last generation of factory carbs had an external vent that had a little stopper door on it so it only vented with the throttle closed. The reason for this leads to the potentially major disadvantage of an always open external vent: it will affect metering of the mixture if the air inlet system has any restriction. Here's how:
An internal bowl vent is exposed to the same pressure as the incoming airstream. Therefore if the air filter or the air inlet plumbing is slightly restricted, the vacuum placed on the vent reduces the head pressure on the fuel in the bowl, reducing the amount of fuel being fed through the jets, thus balancing the reduced air flow with proportionally less fuel. An external vent carb will run rich if the air inlet system is constraining the quantity of air entering the carb.

Unless it's the type of vent that is only open at closed throttle, I always opt for no external bowl vent. My short stint with an old-model 2100 carb- the AFR gauge showed wide variation in the mixture at different road speeds. The bowl was externally vented, and I have a cold air duct which picks up air in front of the radiator support which, at speed, was "forcing" air into the intake system. This threw the metering off because the external vent did not allow the internal vent to read the incoming air pressure and compensate for the different air pressure entering the carb. When I plugged the external bowl vent the issue diminished. There's a reason the new aftermarket carbs do not have a bowl vent.

Ironically, with an internal vent only, excessive airflow restriction will actually make the carb go lean because the vacuum at the surface of the vent is hydraulically multiplied over the entire surface area of the fuel in the bowl.

Get the new bowl without the vent.

 

[DON]

Thanks Frank!! Another lesson in fluid dynamics . After sleeping on it and reading through it at least 3X, I think it has soaked in. It does make sense. Keep a clean air filter, I might have some more of a hot soak problem. I hadn’t even thought about this angle it it does explain why bowels aren’t externally vented in later carbs. I was thinking and worried more about if the bowel over fills( needle valve not closing for whatever reason). Where would the gas how be? Out the enternal vent? I think now that is secondary to the issue of bowl pressure/ vacuum. I might try to over fill the carb with the ventless bowel and see where it comes out.
I do fell good now about going to a ventless bowel, and will keep an eye on the AFM for any changes. A big thanks!

 

[Frank]

I believe the ventless bowl will be fine. If the needle sticks the fuel comes out of the lowest available outlet, which is the main discharge nozzles, into the manifold. Stuck needle flooding is a problem regardless of vent design, so it's kind of a moot point. I was always afraid of underhood fire with a spewing carb, especially on my GM and Mopar 8's with the distributor behind the carb.
I've found that my Holley 390 carb (my first Holley) has minimal heat-soak issues, but it's the old "heavy" metal material, not aluminum. The Edelbrock on the same intake configuration was much worse.

You may see a change in AFR, but probably not assuming your air filter housing system is correct.

 

[DON]

I just know one time the needle stuck and gas was coming out that vent hole. I guess that is a given danger with carborated engines .
I am satisfied that the swap is doable. And I am more aware of what to look for
Thank you!!