Getting ready for synchronizing the carbs

[Andrew Vanis]

The weight of the fluid in the column going from the tank to the carburetors is the issue. A 6 inch column of fuel weighs considerably less than a 6 FOOT column of fuel.

Simplicity! love It!

[Agemax]

The weight of the fluid in the column going from the tank to the carburetors is the issue. A 6 inch column of fuel weighs considerably less than a 6 FOOT column of fuel.

that is a no brainer, the point is a 6 inch column of fuel to the carbs weighs the same if it is positioned 2 inches above the carbs or 2 foot above the carbs. which was my point in the first place, if you care to read it properly!

[Agemax]

Steve is right on this one. The amount of fluid above a specified point determines the pressure exerted by that fluid. Think of it as diving down into a pool of water. The deeper you go the greater the pressure exerted by the water above you. The air pressure exerted on top of the water is the same. In the case of the gas tank, the coulomb of fluid is equivalent to the depth of the water. The more fluid above the point you're measuring, the greater the "depth" and the higher the pressure that is exerted by that fluid. It’s all about the weight of the fluid and not the air pressing down on the fluid from above. Here's a pic that might clear it up:

that picture proves nothing when referring to a temp. tank as the outlet at the bottom will be in the same place, wherever you mount the tank!

[robertbarr]

i was just saying it is fluid under atmospheric pressure, it is NOT hydraulic!

Atmospheric pressure has a net zero effect in this case. It's Rho-Gee-H -- density times gravity times height. It's why divers need special gear and techniques -- so the pressure doesn't kill them, either on the way down or up. It's why submarines have to be built to extraordinary stength -- and even then, the deeper they go, the greater the risk of hull failure.

In fact, pressures are often expressed in terms of height of a column, rather than PSI or kPa -- as in, inches of mercury.

The scientist Pascal (the P in kPa) used to stage demonstrations of this by blowing up wine casks by filling a tall, thin tube attached to the cask with a very small volume of wine -- A liter, maybe. Very wasteful of wine, if you ask me.

[JTGS850GL]

that is a no brainer, the point is a 6 inch column of fuel to the carbs weighs the same if it is positioned 2 inches above the carbs or 2 foot above the carbs. which was my point in the first place, if you care to read it properly!

Your point is understood but still incorrect... The one factor that you're neglecting to take into account is the coulomb of fluid that is in the tube connecting the tank to the carbs. This is a closed system. The higher you place the fluid the longer the coulomb of fluid and the more "weight" the fluid represents. If you move the tank from 2" to 2' you extend the coulomb of water by 1'10" and increase the pressure by the amount of wieght that that coulomb of fluid at that height represents.

I like to take things to extremes to make the concept clearer. If you take that container of gas that's connected to the carbs and move it below the carbs you will create negative pressure and siphon the fluid out of the carbs. If you take that same container and now raise it above the carbs the gas will return back to the carbs and refill them due to positive pressure. If you raise that same container of gas to hundreds of feet up you will raise the pressure of that fluid (Pounds per Square Inch) at the carbs to the point of over riding the float bowl seats and flood the floor with gas.

[Agemax]

exactly my point. you aren't going to fit a temp. tank 100's of feet up! 2" or 2 foot is not going to make any difference whatsoever when connecting it to the carbs.

[JTGS850GL]

This has become more of an academic discussion but I think the point here is that the higher you raise the temporary tank the higher the pressure on the float bowl seats. Raising it higher then normal puts additional pressure on the seats and MAY cause them to inadvertently leak. The 100's of feet scenario is an exaggeration to prove a point, but I'm glad that you at least accept the concept of hydrostatic pressure. In reality increasing the height by 1 meter only puts about 1.02 PSI more pressure at the float bowl seats. The formula is:

p=hPg where

p = pressure (N/m2, Pa)
h = depth at which the pressure is measured (m)
ρ = density of liquid (kg/m3)
g = the gravitational constant (9.81 m/s2)

For gasoline the density (P) is: 719.7 kg/m3

At 1 meter height you get:

p=1*719.7*9.81=7.060257 kPA or about 1.02PSI

Sorry, I love math and physics. Spelling... Not my strong suit.

This may not seem like much, but that's more then what the seat was designed to hold back.

[Agemax]

p=hPg where

p = pressure (N/m2, Pa)
h = depth at which the pressure is measured (m)
ρ = density of liquid (kg/m3)
g = the gravitational constant (9.81 m/s2)

For gasoline the density (P) is: 719.7 kg/m3

At 1 meter height you get:

p=1*719.7*9.81=7.060257 kPA or about 1.02PSI


ok everybody, next time you want to knock up a temporary tank to balance your carbs, make sure you follow this formula strictly. otherwise it wont work as the hydraulic pressure will blow your float valves to bits. YOU HAVE BEEN WARNED!

[JTGS850GL]

Glad you understand it now. Keep in mind that we started out with this as your original statement:

where does the hydraulic pressure come from?????? it is atmospheric pressure acting on the fuel, which will be the same if the temp. tank is 2 inches above the carbs or 2 feet!

From there we are now debating on whether that extra 1psi will really make any difference.

The truth is it may or may not. Just depends on how high you place the gas container and how weak your float bowl valve is.

[Agemax]

i am so glad now too. i never new my old GS had a hydraulic fuel supply system

[JTGS850GL]

Well since your GS uses gasoline and gasoline is a liquid, then yes.

Definition of hydaulics.

Look, I'm just busten your chops. Don't take it too seriously.

[Agemax]

Well since your GS uses gasoline and gasoline is a liquid, then yes.

Definition of hydaulics.

Look, I'm just busten your chops. Don't take it too seriously.

dont worry, i am not, never have and never will. it is really hard to get serious with some comments people post up on this site lol. thats what makes it so entertaining

[Brendan W]

Anybody want to buy $1 plans for a diverter valve from the nitro bottle to pressurise the float bowls. You can put the gas on the roof if you want but will need the solid float conversion kit at $200 plus tax.
Here's a brain teaser. Is the fuel level different when the gas tank is full or empty and if not, why?

I'm getting ready for carb balancing as soon as the last shim turns up. I'm just above .03 on three valves and a whisker below on two.

My old '83 Carbtune is dusted off and ready - just need new adaptors. Correct me if I'm wrong but they are 5mm, yes?

[tkent02]

Anybody want to buy $1 plans for a diverter valve from the nitro bottle to pressurise the float bowls. You can put the gas on the roof if you want but will need the solid float conversion kit at $200 plus tax.
Here's a brain teaser. Is the fuel level different when the gas tank is full or empty and if not, why?

I'm getting ready for carb balancing as soon as the last shim turns up. I'm just above .03 on three valves and a whisker below on two.

My old '83 Carbtune is dusted off and ready - just need new adaptors. Correct me if I'm wrong but they are 5mm, yes?

I think it's 4mm, but not sure.

[Agemax]

the adapters are 5mm.