Carb sync opinions

[dbeardslee]

That's assuming that 2cm of travel of the steel bars inside a carbtune is the same as 2cm hg, which it's not. Each line on the carbtune represents 2cm hg - says so right in the manual. I don't have what's left of my mercury sticks anymore, but IIRC the graduations on them were farther apart than on the carbtune, and it seems to me they were graduated in inches of mercury. And it all goes out the window if you're using trans fluid, as I have no idea what that relates to in cm hg. I'm guessing that when Torricelli first came up with the idea of measuring vacuum with mercury, the diameter of the tubes he used was probably smaller. According to the carbtune manual most carbs should be balanced withing 2cm hg, but some only need to be balanced to within 4cm hg. Just depends on how your sticks are graduated as far as measurement is concerned.

[fredintoon]

- - - I'm guessing that when Torricelli first came up with the idea of measuring vacuum with mercury, the diameter of the tubes he used was probably smaller. According to the carbtune manual most carbs should be balanced withing 2cm hg, but some only need to be balanced to within 4cm hg. Just depends on how your sticks are graduated as far as measurement is concerned.

Back to school for you Doug,
The fluid column height depends only on the fluid's density, not the column's diameter. See "Pascal's vases"
To approximate, atmospheric pressure of ~15psi will support a Mercury column ~30" high.
Thus 3/4" of Mercury is ~ 3/8 of a psi.
Is this close enough to balance the carbs?
I dunno.

[dbeardslee]

Fred - my point was that with a larger diameter tube, the same amount of vacuum isn't going to raise the column as much as it would in a smaller diameter tube - regardless of the fluid that's in it. Then again, maybe it will as you've got more volume for the vacuum to fill. I'm gonna have to test that theory. Then again, the cylinder is going to pull a relatively fixed amount of vacuum, so in order to create the same vacuum in a bigger diameter tube it would have to draw more - right?

[fredintoon]

Fred - my point was that with a larger diameter tube, the same amount of vacuum isn't going to raise the column as much as it would in a smaller diameter tube - regardless of the fluid that's in it. Then again, maybe it will as you've got more volume for the vacuum to fill. I'm gonna have to test that theory.

Hi Doug,
no need to test.
Blaise Pascal did it for you back in the 18th Century.

http://www.oberlin.edu/physics/catalog/demonstrations/fluids/pascalvases.htm

[dbeardslee]

Fred - so here's my question - what happens when you apply the same amount of vacuum at the top to each of the different sized tubes? Is the fluid going to move the same amount in each tube?

[cywelchjr]

Hi Doug,
no need to test.
Blaise Pascal did it for you back in the 18th Century.
http://www.oberlin.edu/physics/catal...ascalvases.htm

That just shows that given them being connected the water will go to the same level. A given amount of pressure or vacuum will lift a given amount of weight, if the column is wider, it will be heavier and will not rise as far. That's why everything in mercury sticks has to be carefully calibrated, so it's the same diameter and the same amount of material in each tube, or they won't come out the same. We learned that back in 6th grade science.

[dbeardslee]

Thanks Cy - I always hated school, and the idea of going back was sending a shiver up my spine .

[fredintoon]

I see more clearly now

Hi Doug, Cy,
OK. Pascal's vases demonstrate that the levels in a connected open system are independent of the volumes in it's different parts.
BUT
a U-tube hooked up to two different vacuum sources (or a 4-way to four of them) is a closed system.
Just like hydraulic brakes where Pressure x Area is a constant.
So if the fluid columns ain't the same size the same reduced pressure on each column will not bring them to the same level.
It's been 60 years since they beat this stuff into me and some of it is getting blurred.

[cywelchjr]

Hi Doug, Cy,
OK. Pascal's vases demonstrate that the levels in a connected open system are independent of the volumes in it's different parts.
BUT
a U-tube hooked up to two different vacuum sources (or a 4-way to four of them) is a closed system.
Just like hydraulic brakes where Pressure x Area is a constant.
So if the fluid columns ain't the same size the same reduced pressure on each column will not bring them to the same level.
It's been 60 years since they beat this stuff into me and some of it is getting blurred.

Right, that's just what I was saying. It's not been as many years for me, but it's still been about 40 of em. I just remind myself that the fluid has weight, and with a fatter column it takes more pressure to move it as far because your moving more weight, which is why Psycoreefers bike is faster than mine, it has to move less weight! (well, that and the fact that his is a 79 and mine as an 80).

[Ken Talbot]

A given amount of pressure or vacuum will lift a given amount of weight, if the column is wider, it will be heavier and will not rise as far.

But with the amount of vacuum or pressure, which is measured in X units per square inch, you get more square inches of that vacuum or pressure operating on the column. Net result is the same amount of lift no matter how narrow or wide the column. It just make take a bit longer for the vacuum being supplied by a narrow tube to evacuate a larger cylinder to achieve the lift.

[dbeardslee]

But in our application it would take longer to achieve the same vacuum for a larger volume, and our vacuum source remains pretty constant. One stroke of the piston is all you get .

[DGXSER]

Yep just like Ken put it, it can take little longer to create the pressure or lack of it, but the measurement will be the same no matter the diameter. pressure, or lack of it, is equal across a system. That is why you can make that big huge pvc pipe canister plenum in the tech tips and still get accurate and the same measurement of the bikes vacuum being created. As if it were not there. So a bigger diameter tube say 1" versus a 1/2" will still read the same vacuum level in both. See, for once in our lives size REALLY does not matter!!