Fuel "foaming" in float bowls problem

[toolmakeron]

I hope to get some input why the fuel in a Holley carb is "foaming" in the bowl. It shows clearly through the sight glass. What causes this & what are the cures? I saw this on a chassis dyno run, & we are thinking that the regulator is too small. Probably going to two regulators.Is a bypass necessary for preventing this? Application is a BBC 540 ,drag race, 13.5, solid roller.1250 Holey. On an engine dyno it made 925 hp,all seemed to be ok. Now, while filming the carb on the run, we see this & stopped . I saw a U Tube with a BLP modified bowl that showed their fix for this problem, but I didn't see why it happened. Appreciate the help guys, thanks.

[BOOT]

BLP has a anti foam dual reg bowl kit, Quickfuel has dual N&S bowls, APD has some new bowls as well.

[bigfoot584]

Here's a comparison between a .110 NS on the left at 6.5 PSI
and .250 NS at 2.5 PSI on the right.

https://www.youtube.com/watch?v=zftUFW9MfrM

It has something to do with the shearing action coming thru
NS that create a lot of the problem, increase seat area and
reducing PSI helps reduce this.

This may helps some also.
http://racingfuelsystems.myfunforum.org ... ut688.html

[MadBill]

There are several potential causes. Beyond the above there's the 'roiling' action of spraying the fuel out above the liquid level, addressed by N&Ss like this: http://www.4secondsflat.com/FBO%20Carb%20Parts.htm There is also sometimes engine vibrations that excite the fuel at certain RPM ranges, for which there are rubber base gaskets and cushioned washers for the retaining nuts, to damp out the relevant frequencies.

[Adger Smith]

You can also put about a .060 bypass hole in the inlet up near the carb inlet to let all the air coming out of the regulator to escape. I do mine at the center of the Y block for the front & back bowl feed lines off the regulator. I have another one that comes off the side of the regulator on the outlet side. You would be surprised how much air comes through regulators. You want a solid slug of fuel going through a N&S. If it isn't it just exaggerates the aeration.

[Racing68]

Found this.

https://www.youtube.com/watch?v=3aVEwud70I4

[powellmachine]

braswell has a ball nose n&s that really helps with foaming

[Alaskaracer]

You can also put about a .060 bypass hole in the inlet up near the carb inlet to let all the air coming out of the regulator to escape. I do mine at the center of the Y block for the front & back bowl feed lines off the regulator. I have another one that comes off the side of the regulator on the outlet side. You would be surprised how much air comes through regulators. You want a solid slug of fuel going through a N&S. If it isn't it just exaggerates the aeration.

Can you post pics of this? I'm interested in it.

[DaveMcLain]

Found this.

https://www.youtube.com/watch?v=3aVEwud70I4

I saw this at the PRI show.. I seems to me that Willy is somewhat exaggerating the foaming problem with his test rig....

[Kevin Johnson]

https://books.google.com/books?id=bzhwW ... ir&f=false

Perhaps ~70ppm of dissolved oxygen in normally handled racing fuel at sea level would be a reasonable estimate as well. In conditions where the liquid was exposed to less than ambient pressure this dissolved gas (and other atmospheric gases as well) will evolve. This is apart from volatile fuel fractions that can also evolve.

[jmarkaudio]

On car dynamics of a float bowl on Mike Laws/BLP 6 second dragster. First part is a standard bowl with foaming showing, second is their new style.
https://www.youtube.com/watch?v=s-q1eJu1Wz8

Dyno vids, first a standard bowl, second the new version.
https://www.youtube.com/watch?v=PehQUKwQX8E
https://www.youtube.com/watch?v=FOJKcvTKQAg

[Racing68]

Found this.

https://www.youtube.com/watch?v=3aVEwud70I4

I saw this at the PRI show.. I seems to me that Willy is somewhat exaggerating the foaming problem with his test rig....

Ya it looks like his fuel pressure is way over the normal. Probably in the 15-20 range for dramatic effect.

[BOOT]

You can also put about a .060 bypass hole in the inlet up near the carb inlet to let all the air coming out of the regulator to escape. I do mine at the center of the Y block for the front & back bowl feed lines off the regulator. I have another one that comes off the side of the regulator on the outlet side. You would be surprised how much air comes through regulators. You want a solid slug of fuel going through a N&S. If it isn't it just exaggerates the aeration.

Can you post pics of this? I'm interested in it.

Also interested, can't really picture what your trying to say. Also I've herd a larger than needed size inlet line helps separate the air bubbles after the reg.

[Adger Smith]

Car is Unavailable for pictures. I'll try to draw it out tomorrow, Bed time now. Tim Cole @ Comp Cams has the same setup on his V-6. We both had problems that it corrected. He might have a picture.

[Kevin Johnson]

Also interested, can't really picture what your trying to say. Also I've herd a larger than needed size inlet line helps separate the air bubbles after the reg.

The flow can stratify by density. That is an old trick used in many deaeration devices. The same effect had disastrous consequences for the Porsche 944 and 928 engines because it supplied a locally biased greater percentage of entrained air to particular circuit branches.