How to build a water manometer

[Guest IanJ]

This is a "reprint" of a post I made in the technical forums, that seemed like a good "howto" item.

 

I use a water manometer that I constructed out of about $1.50 worth of plastic tubing and 5 feet or so of PVC pipe I had lying around. It is more sensitive (read: easier to see small differences) than a mercury manometer, and has a TwinMax beat on sensitivity, reproducibility, and price. The serious disadvantage? It's over 5 feet long, and doesn't travel well. (Well, and it's not a cool gadget.)

 

To make a water manometer, get about 20-25 feet (6-7.5m) of clear vinyl tubing which has the correct inner diameter to go over the vacuum nipple on your bike's throttle bodies or carbs. Fold the tubing into a thin U shape, but don't pinch the bottom -- it needs to allow water to flow freely to work right. Attach the bottom 5 feet (1.5-1.8m) of the U to some kind of stiffening structure. PVC pipe, wooden dowel, piece of lumber, the wall of your garage, you could even just hang the thing loose from the upper attachment point in the drawing below, the choice is yours. I used nylon zip ties to attach mine to a thin PVC pipe. The main thing is to have a length of tubing with this U shape, ideally with the sides of the U lying right next to each other for comparison. There should be enough tubing coming out of the top of your manometer to reach both carbs or throttle bodies on your bike -- mine has about 6 feet on each side.

 

See this drawing of a manometer for a visual representation of what I'm talking about.

 

Now, add water to the tube. You need to fill it up so there's water up to about 3 feet (1m) inside the U, so you have a foot or two of clear air above the water when it's at rest. That gives you enough room for the cylinders to be significantly out of balance and still not suck in any water (when the water reaches the top of the U and starts down toward the carb, you'll get a quick cleansing burst of water through that cylinder and have to refill your manometer). I found that using a vacuum pump (or sucking on the tube) with one end submerged in clean water works alright, although I spent about 20 minutes getting bubbles out of the tube on mine.

 

Attach the sides of the manometer to each cylinder and test away. A higher level in one tube or the other indicates that that side of the engine is pulling more vacuum than the other side. The only important difference between the water and mercury manometer is that this simple model can only compare two carbs at a time -- not an issue on two-cylinder bikes, though, and three- or four-cylinder bikes can just compare carb 1 to carb 2, then carb 1 to 3, etc. Oh, and sucking water through one cylinder won't cause any harm or mental degradation, unlike vaporizing 300 ml of mercury. Water also doesn't run out of batteries.

[Guest Brianuk]

I found it better to add automatic transmission fluid, rather than water. First time I tried it with water, the two sides were so far out that the water had been pulled into one cylender before I could stop the engine. ATF does less damage.

[Guest HI-TECH-CHECK]

Oh, and sucking water through one cylinder won't cause any harm or mental degradation, unlike vaporizing 300 ml of mercury.  Water also doesn't run out of batteries.  

Unless,it hydro-locks. Then you got real problems.

[Guest Knud]

HELP!!!!!

I have the same problem with the misfire on my 2003 V11 LeManns Catalyzed version. I have also the impression that the engine is getting to hot due to the lack of gas. This has already caused 3 sets of broken sparkplugs & now the 3rd ECU & a broken manifold within the first 4000km. Since 2003 it is not longer possible to adyust the ECU :finger: What can I do?

 

Regards

Knud