[Tom Vaught]

"Engineers do stuff for reasons"

This afternoon and maybe tomorrow will post up some info I posted on the Motorsport Village Website years ago.
They actually gave me credit for the info.

Info is from Tom Vaught, former Holley employee.

1) Why the Holley Hex Nut above the the Float Bowl has 6 sides (vs say 8 sides):

The thread used on the needle and seat that screws into the top of the float bowl is a 3/8-32
thread. There are 32 threads per inch cut on the needle and seat where it goes into the bowl.
One full turn of the Hex Nut will move the needle and seat 1/32” or .03125”
or for easy math about .030” upward or downward.

2) What the actual float movement is vs the tip of the needle (away from the seat):

The float has a 6 to 1 multiplication ratio so you turn the needle and seat hex nut one full turn downward, the float movement will be .03126 X 6 or .1875” lower in the float bowl and the average fuel level in the bowl will be for easy math .180” lower. Two “Flats on the Hex nut works out to about a 1/16” of fuel level change in the float bowl. If you keep accurate records of your float level position you can track the air/fuel ratio change (with an accurate air/fuel meter and get the fuel bowl fuel level vs the mail well fuel level dialed right in for your intake manifold/ carburetor/ engine installation angle dialed right in for best fuel control.

3) Why the fuel level rises in the bowl, (above the Holley Calibration Level), when a higher fuel pressure (vs the Holley fuel pressure spec of 6 psi) is used:

When the needle and seat (.110” size) is used with a factory float bowl and at the Holley fuel pressure calibration point (6 psi), the average float level height will be close to the “design fuel level” in the bowl and and the carburetor will will meter fuel properly. In some of the old Holley Books they used to show an external gage mounted on the fuel bowl to check fuel level before the “Sight Plug” type bowls were designed. If you add extra fuel pressure to the fuel line going to the bowl the needle and seat will have a higher pressure acting on the tip of the needle and seat. A small change here in force acting on the tip of the needle vs a fixed float buoyancy force X a 6 to 1 float ratio mentioned above means that the FUEL LEVEL IN THE BOWL WILL RISE TO A NEW AVERAGE LEVEL WITH INCREASED FUEL PRESSURE.

4) Why the fuel level rises in the bowl, (above the Holley Calibration Level), when a larger needle and seat is used (vs the Holley .110 needle and seat).

In the previous paragraph 3), the fuel level went up because the pressure on the float was higher due to the fuel pressure.
The other way the level can go up is by using a larger area needle and seat which also imparts more force against the float,
(raising the average fuel level.

A Holley 6-504 part Number is Holley's standard .110” Viton Needle and seat assembly
A 6-505 needle and seat will flow about 170-180 lbs of fuel per hour at 7 psi (depending on the specific gravity of the fuel used).
175 x 2 = 350 lbs of fuel per hour. About 630 horsepower if assuming a .55 lbs/horsepower/hr.

Using the larger needles and seats naturally will move more fuel BUT fuel level changes in the bowl will have to be monitored for
each combination vs expected air/fuel ratio and driveability.

5) Why “Float Drop” is important:
If you have the wrong float drop, the float can “hang” against the needle as it rides on the “hump” on the float level. There are two needle and seat lower needle dimensions. One needle has a 2 cm lower diameter and the other one has a 4 cm diameter. Naturally the 4 cm diameter needle and seat will not “hang” as easily as the “footprint” (diameter) is twice as large. If the float “hangs” you will have open flow into the bowl with no fuel control and flooding, fuel coming out of the vents, and potential “hydra-locking” of the engine. As second issue with the wrong float settings is that the fuel level in the bowl could be too low and uncover the power valve on acceleration. Special power Valves can help eliminate this issue.

6) Why Floats collapse after a Carburetor Fire:

If you have a carburetor backfire, and the carburetor is burning inside the venturis, the main-body gets hot quickly. This heat transfers to the air in the carburetor heating it and the also to the parts around the air. The brass floats have air inside of them when they were made. The air in the float gets hot, expands, and trying to get out of the float. Many times there are very small places where the air can escape but fuel cannot get into the floats. As soon as the engine is restarted, the cold fuel enters the bowl, the float is still hot. The float cools rapidly vs the lost air inside the float. Because the air pressure outside is now higher vs the inside of the float the float collapses (just like it would under boost). Now you have a big problem. The black Nitrophyl floats do not suffer this problem therefore as we know are a better component to use in a boosted carburetor. At least now you can explain to your buddy why his float looks like Chit when he was not running any boost through the carb, LOL!

7) What the “Standard” Brass Float should weight vs what the Black Nitrophyl Float weighs:

A Brass float weighs around 15 grams. (An average paper clip weighs 3 grams). The black nitrophyl float weighs about 11 grams. When you cut notches in the black float to allow for jet extensions, (or if you buy a black float with the notches already there), you should check the weight of the float on a gram scale to see if it is close to the right factory weight. You never know how much epoxy the guy used sealing the float, how deep he made the cuts, etc. Some floats for the road race guys and NASCAR guys are heavily modified. If the float is too light, (less than 11 grams stock, or if you want to make the float the same weight as the brass float you can add extra lead shot to get up to the brass float weight of 15 grams.

More on this tomorrow. I actually posted 16 pieces of info on the site. You got 7 today Part 2 tomorrow

Tom V.