Calling all Physics boffins - BMW Luxury Touring Community
 
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post #1 of 5 Old Nov 10th, 2006, 8:45 am Thread Starter
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Calling all Physics boffins

During the last week or two, a buddy and I have been using a rather nice set of Carb balancing gauges which we had on loan (not on my LT). While working on the bike we got into a discussion about home made "Heath Robinson" devices for doing the same job as the 70.00 gauges. We both agreed that a set of tubes filled with water would work very well, but got into discussion about optimum tube size to maximise the accuracy of the level change.

Given that the same Vacuum is applied to point A on the tubes, which water level will change the most? 5mm tube, 10mm tube, or will they both move the same. -see picture-
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Mike

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post #2 of 5 Old Nov 10th, 2006, 9:08 am
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I don't think it would make much difference given the tube sizes you describe if you are only interested in the difference between the two readings and not in the absolute value of the readings. You might find this article interesting.

Res ipsa loquitur, sed quid in infernos dicet?

Alan Stuber
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post #3 of 5 Old Nov 10th, 2006, 9:45 am
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Vacum gauges

Mike

I think the issue may be more the 'lift' that can be exerted which is why they use mercury(?)

$4 gauge advice here:

http://www.airheads.org/content/view/183/98/

Graham Wintersgill
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post #4 of 5 Old Nov 10th, 2006, 9:53 am
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Quote:
Originally Posted by myk_edwards
During the last week or two, a buddy and I have been using a rather nice set of Carb balancing gauges which we had on loan (not on my LT). While working on the bike we got into a discussion about home made "Heath Robinson" devices for doing the same job as the 70.00 gauges. We both agreed that a set of tubes filled with water would work very well, but got into discussion about optimum tube size to maximise the accuracy of the level change.

Given that the same Vacuum is applied to point A on the tubes, which water level will change the most? 5mm tube, 10mm tube, or will they both move the same. -see picture-
Diameter of the tube makes no difference, both will read the same difference in height of liquid in the tube, no matter if it is a very small tube, or a very large one.

Water is not used for carb balancing as the height of the column would have to be quite large. If you have 15" of Mercury vacuum reading (common at near idle), that will be 204" of water! Someone would have to stand on a ladder to read the top column height.

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post #5 of 5 Old Nov 10th, 2006, 6:42 pm
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Quote:
Originally Posted by myk_edwards
During the last week or two, a buddy and I have been using a rather nice set of Carb balancing gauges which we had on loan (not on my LT). While working on the bike we got into a discussion about home made "Heath Robinson" devices for doing the same job as the 70.00 gauges. We both agreed that a set of tubes filled with water would work very well, but got into discussion about optimum tube size to maximise the accuracy of the level change.

Given that the same Vacuum is applied to point A on the tubes, which water level will change the most? 5mm tube, 10mm tube, or will they both move the same. -see picture-
Don't use water! If you do you'll suck a lot of water into your engine.

I made a 6 tube manometer to use on my 6 cyl Honda CBX. I used 6 glass tubes, 1/8 inch ID, mounted to a board with graduations. The bottom of the tubes are submerged in a Mercury filled reservoir. The top of the tubes are attached to clear tygon tubing that goes to the carb synchronizing ports. Works very well.

Bruce Hodges
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