Mark's BMW R 75/5 Web site

My Experience Building and Using a Home Made Manometer

The manometer I built. Use water, not oil for the liquid.
I built the manometer shown at left. I used translucent plastic tubing from the hardware store. I used duct tape to hold it to a verticle piece of wood. I used a 2x10 block of wood for the base so that it would be stable - it is.

At first I attempted to use automatic transmission fluid for the liquid. I have some old Fordmatic transmission fluid that is bright red and I thought the viscosity would help damp the motion. It turned out to be very difficult to pour it into the tube and have it run down. I wound up washing it out and using water. Water is easy to get to flow into the tube, and a little food coloring makes it red enough to easily be seen (you can see the red fluid in the picture.)
I attached rubber vacuum hoses to the plastic tubing because the rubber tubing is more flexible and easier to get where it needs to go to attach to the bike. It worked out well.

The final touch was to use a piece of 3/16" wooden dowel rod with a 1/16" hole drilled through it end to end to make a restricter. I placed this at the end of the 8' long vacuum hoses. During use on the BMW, the fluid moved slowly and smothly in the manometer, it did not vibrate or jump around with each stroke of the cylinder. The BMW carburetor has a small opening in the carburetor wall, which serves as a restrictor and that may account for the damping more than the restrictor I made out of dowel. We'll see when I put it on the V-Star.