Just finished up my $5 carb sync tool, actually it's more like $15 as I had to replace two plastic T's with brass cause I broke them.

I am having some trouble getting it to work.  I attached the tubing to the carb tops, and started up the bike fine.  Then all the water, slowly leaked out of the system and into my engine.  Is this an air leak in my design somewhere??  That's what I am going with, but thought I'd ask first.

How do I get the water to stay in the loop?

Wouldn't the T valves somewhat equalize the pressure between both carbs?

That amount of water doesn't weight much. If one carb has higher pressure, it will push the water into the other one.
You would need something heavy enough that a slight pressure difference wouldn't shove it from one side to the other - like maybe a 3' column of mercury, or maybe a spring loaded diaphragm. Maybe a low pressure tire gauge on each side and read the difference? Something, as that little bit of water can easily get blown from one side to the other.

Pipe organ experience suggests you could easily make a small bellows from 2 sticks of wood and a scrap of leather. A spring or weight on it would regulate it. Make 2 of them and balance them the same. Open your "T" and valve would help insure both were calibrated the same, then close it and see how high each one goes. While it may not give you a PSI reading, it would show if they were different. For measuring vacuum, reverse it and have a spring hold the bellows open and the vacuum sucks it closed. Pipe organs and the pneumatics of them give lots of ideas. East to fabricate with squares of wood, scraps of soft leather (have lots of that) and some glue.

When I built one, I used 2 stroke oil. 60+ weight engine oil should be fine too, though. Not the end of the world if a little is sucked in. I have the motion pro non-mecury 4 cylinder carb sync tool - they install restrictors in each vaccum line to even out the power pulses, and slow the response of the gauge to major imbalances. Might be worth trying if you can find something suitable.

I made mine kinda like that, 4 cylinder tho, for my katana, I used transmission fluid in mine. also, you should try removing the aquarium valve and use a denser liquid. also make sure you dont have any air leaks in the system, or it wont work right.

I've had the water sucked in before too...didn't do any damage. Did you check the o-rings?

O-rings are new.  I may try to get some tranny fluid AND lengthen the Loop.

Like burning1 mentioned, I think you need some restrictors in the lines to reduce the pressure to more manageable levels. Then you'll still get a reading, but it will be gentle enough not to suck in the water.   Not sure what to use, they will need to be exactly the same for each side. Maybe or bead or something similar jammed into the tubing? I'd stick with water if possible, it sounds much easier to clean up when you are done. And yea I think a longer loop will help, too.

Make sure to start with the valve as far open as it can go also.  The carb that the water gets sucked into is the one with more vacuum.  Adjust the carbs accordingly.  I would stick with water so that nothing else weird gets sucked in.  Oil is less dense than water so that will actually hurt you as far as getting sucked in.  A bigger loop is the way to go and open up the valve until your carbs are close to balanced and you need more sensitivity.

Thanks guys,

Got it working with a 10ft. loop and some gear oil.  She runs!!