Mercury Carb stix are best, motion pro were good and reliable for years, but must be bought used. DON'T BUY THE NEW MOTION PRO CRAP! Made the list at #3 of the worst tools ever made out of 6,000,000. If buying new get the Morgan Carbtune out of England. Don't buy the new motion pro for sure. I could go on for hours about the motion pro, but will end it with DON'T EVEN THINK OF BUYING THIS FRICKING THING CALLED A TOOL.
321,000 miles on KZ's that I can remember. Not going to see any more.
Back in the day I made my own mercury gauges and they worked great. In these day and times I strongly recommend the Morgan Carb Tune. It's easy to work with and reliable. Much better than messing with some round vacuum gauges, which I've also used.
The manometer type - either mercury or other fluids - are self calibrating (as opposed to multiple dial types which may or may not be calibrated to each other at any given time). I use a Morgan carb tune but I've never check the calibration of the individual tubes/slugs against each other so don't really know how close they are.
Have also used the MotionPro unit and while I don't find anything wrong with it's design or performance, it's not a tool that I use every day - I've have found the few times I did go to use it, the fluid had dried up. I ended up having to keep spare bottles of fluid on hand. I probably should have just tossed the MP fluid and used transmission fluid or something like that.
Keep in mind, if you have CV carbs, synchronizing really only affects the idle (not that that's a bad thing), or perhaps more accurately: synchronizing has most effect on the idle.
Below is a post I made in that thread. Cheap as chips and 100% accurate.
"Guys, as I said I only borrowed the carb tune pro out of curiosity to see if they were as accurate as I remember the mercury ones being. They dont appear to be so without some trial and error set up. I moved onto the ball bearing hoop method after my original set died.
If anyone is unaware of this method I will explain with the aid of some pics.
The inner ring is sealed and the ball bearing hangs centrally under gravity and is your datum point. Pic 1
The outer ring is open at both ends. Attach one end to the base setting carb, normally number three. Attach the other end to carb one. Start the engine and adjust the idle to about 1500 /2000 rpm. If carb one is out of balance to carb 3 the outer ring ball bearing will swing to one side or the other depending on wether there is more or less vacuum. Pic 2.
Adjust your slide so that the outer ring ball bearing is back centrally directly under the ball bearing in the inner ring. As in Pic 1.
Do the same for carb 2 & 3 and 4 & 3. Your carbs are now perfectly in sync. Beautifully simple and 100%
There is a piece of tube inside either side of the indicator ball bearing tube which has a smaller internal dimension than the ball bearing so the indicator ball bearing can not come out of the central portion of the outer indicator tube.
The inner tube is sealed and the ball bearing in the inner tube is just the datum indicator.