Mercury manometer

I have a 4-carb mercury stick for carb synchronization.
Yes it is old, I bought it in the 80's, not sure when they stopped using mercury.
I should have taken a picture but after a minute with the motor running it develops breaks in the columns of mercury so there are air spaces.
I have to keep shutting the motor off periodically, once I do the columns return to solid mercury lines.

What is going on?
I Googled mercury contamination with water but all I get is information about water contaminated with mercury.
Is the mercury contaminated with something?

 

Likely not contaminated, just too much vibration and airflow.... a Carbtune comes with "restrictors" which are smaller pieces of tubing you insert in your hoses, this reduces the volume of air and fluctuation, but still the same amount of vacuum is attained. Might want to try necking down those hoses?
BTW, I have never tried the mercury version

 

It has restricted orifices in each tube.
Worked great in the past.

 

It's a Motion Pro.
The only thing I can think of is maybe the mercury level is low.
Where can I buy more mercury?

 

I would think if all your mercury levels are the same when engine not running, it's OK.... no idea where to get mercury.

 

Remember my manometer project? Homemade Manometer
I put restrictors in the tubing and the mercury is very solid when in use. It is strange that your commercial product used to work correctly but now doesn't.

 

This is from the Web:
Bubbles in a mercury sync tool (manometer) occur when air is sucked into the tubes during the carburetion sync process, usually caused by failing to use restrictors, too high engine RPM, or improper venting. The high vacuum pulls air into the mercury column, making the fluid bounce, which makes accurate readings impossible