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Several have done it but it isn't the best method. Only the cheapest. I like the baby jar with red fluid option.
 

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It will work, but you need to put a restrictor in the tubing that has a tiny hole to dampen the vacuum signal. The hole should be .020 to .025. Without these the fluid will bounce around so bad you wont be able to get a smooth reading.
 

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I disagree, I feel it is the best method. I have almost the exact setup shown on that page. I use oil in my manometer. If it gets sucked into the engine, no big deal, its just a bit smokey. The fact is, a difference in vacuum that you could not even see with mercury manometers, will show up as about a foot difference with oil. They're much more sensitive. Vacuum gages are even less sensitive than mercury.



Also, I don't need a limiting orifice, the oil moves really slowly thru the tubing. You have a LOT of time to react to a way off balance condition.
 

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Ideally I'll just build one of these. The sensor I'm using for an illustation is just that, you can find true two-port differential sensors on the surplus market pertty cheap at times. Alternately you could use two that read into the vacuum area and compared their outputs.



http://www.mouser.com/ProductDetail/Freescale-Semiconductor/MPX2053DP/?qs=r8OyiFxb6Re8W6iI/vf66A==



One hose from one port to one carb, other port to the other. Hook up a sensitive multimeter to the output and adjust the carbs until you read an output that equates to both tubes being at an equal potential.



You'll need either one sensor that can register as a differential gauge or two that are designed to read either gauge or absolute. They will need to be able to stand some vacuum on the input, or in the case of using gauge or differential sensors they will need to be designed to read in the vacuum area.



A bit complicated for the normal wrencher, simple for one that also has a bit of electrical circuit knowledge in building small circuits on perfboard.



You certainly aren't going to get any more accurate, and this would be how they build the expensive ones.



All in all, for our purposes a pair of safety catch bottles and two pieces of fluid filled aquarium hose stapled to the wall side by side is going to be plenty accurate for our purposes.



I just like to build things, and given the right sensor(s) at a surplus price a handheld meter would be far easier to set up and portable as well.
 

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I made something very similar last year, I used water with food colouring for a medium. Instead of one constant piece of tubing, I used connectors at the top, which acted as restrictors I guess because I had very little bounce.







I zip tied, the tubing to a drywall T-square, and zip tied the apparatus to a ladder to hold it. My aux fuel tank sat atop the ladder. Here is a crappy cell phone shot of the rig.



 

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I built the yard stick model (using ATF fluid) and had problems with the one side being sucked up to the engine. Made a restrictor from a flat washer to pinch close the two tubes but that was ineffective. Read Larry's recommendation on the restriction of 0.025 inches and am going to try that next. Water has been used, as it reacts faster than oil or mercury.



The twin bottles Blindstich pictured is also an easy project. The part # Marshall posted is what I have been looking for! But, will it work with vacuum? It looks to only work on positive pressure?



On ADVRider there is a thread about shorting out the ignition at the spark plugs. Anyone try that method? Or disconnecting the wires to the coils?
 

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A easy way to restrict the tubes is to clamp a small Vise Grip on the tubes and turn the adjusting nut until it squeezes the tube the right amount. A small "C" clamp would also work. I did this before I got the Morgan Carbtune.
 

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A easy way to restrict the tubes is to clamp a small Vise Grip on the tubes and turn the adjusting nut until it squeezes the tube the right amount. A small "C" clamp would also work. I did this before I got the Morgan Carbtune.


Once you've been,"Morgan Carbtuned" you can't go back<grin>
 

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Has anyone here tried anything like this? How did it work?



http://www.650ccnd.com/mano.htm


I worked for about 17 years as an industrial instrument technician. This is absolutely the most accurate method of measuring differential vacuum. I always used expensice commercial manometers, but this simple system is as accurate as anything that you can buy. I would use a synthetic 2-stroke oil in the tubing. that way if you screwed up and let some oil into the carb it would do more good than harm. And I would use a damper of some sort. Simplest way to dampen it would be to use a simple thumb screw clamp that you can pick up wherever aquarium supplies are sold. You only need to put a restrictive clamp on one line.



The two bottle system is also good but it cannot be read as accurately. Note that the two bottle system is not a guarantee that you can't suck fluid into one carb. If one of the vacuum tube got disconnected while the motor was running it would suck all the fluid into one bottle and some would very likely get into the engine.



The Mouser unit will work with either vacuum or very low pressures. You'll need to have a multimeter, or you could jerry rig a couple of flashlight bulbs and a flashlight battery too detect the movement of the diaphragm. It's just a simple diaphragm which separates the two sides. They claim an accuracy of + or _ 0.5%, which isn't bad but you can do better with a tube manometer.
 

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The part # Marshall posted is what I have been looking for! But, will it work with vacuum? It looks to only work on positive pressure?


The spec sheet doesn't say if it will put up with a vacuum but being a true differential it should to some extent. I'd either write the manufacturer or find their actual full line catalog to see if they have anything that more closely fits the bill. Honeywell also makes a full line of sensors and Motorola (now ON Semi) used to as well. They're out there somewhere.
 

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I understand the tools to measure the difference between the two carbs BUT my question is where and how do you connect it to your carbs?

I set mine up when I had the carbs off the bike and adjusted to get the butterfly's in line don't think It can be far off.
 

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I understand the tools to measure the difference between the two carbs BUT my question is where and how do you connect it to your carbs?

I set mine up when I had the carbs off the bike and adjusted to get the butterfly's in line don't think It can be far off.


On your intake tracts between the carbs and heads, there is a small screw right before the head. It is a 5mm thread, and you need an adaptor that threads into the hole. Some have drilled brass screws, or plastic screws to make their own, I ordered mine, a set of 4 for about $12 IIRC.
 

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I built this exact same yardstick model and it works great. I used 80 weight gear lube. It reacts a little slower than ATF and I have never had a problem with it getting sucked into the carbs.
 
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