Just my opinion but.... I would not buy or use any tool with fewer readouts than the number of cylinders that the bike has. I synch. six cylinder engines with two separate four tube manometers side by side. As these work on physics rather than calibration or adjustment, as long as they are at the same vertical height, all tubes will read correctly even across two manometers. Four cylinder vacuum gauges are easy enough to get that I would not consider a twin gauge and jumping between two cylinders with each gauge. When you make an adjustment on one T.B. or the balance screw between T.B. #'s 2 and 3, ALL the T.B. vacuum levels will change. It is really pretty important to watch all cylinders at the same time. For example, say #3 is high: as you are adjusting that one down, all the others will rise in vacuum and not necessarily evenly either. So if you cannot watch the other three, you would not know which one is highest and lowest.
I believe the carbtune tool uses sticks of metal (a hard metal, not liquid mercury) that are drawn up in the tubes by venture vacuum. As long as the metal sticks and the tubes are all made to very close tolerances, that tool should work fine. It would be easy enough to connect all four tubes to one vacuum line and check the calibration although there really is not any adjustment.
Mercury manometers have been around forever because they work so well. And they work on pure physics without any need or even the ability to calibrate them. As long as there is gravity on Earth, mercury manometers are self calibrating and extremely accurate. Yes mercury is toxic but only if it 'gets away'; if the manometers are handled <reasonably> carefully the mercury will not spill. We all handle a lot of gasoline pretty freely without any repercussions as long as we are reasonably careful with the stuff. I understand the move away from mercury balance sticks and really it is a good idea but still the original mercury types work very well although they do demand more care than a similar device carrying something like anti- freeze (ethyl glycol) or colored alcohol.
Even four vacuum gauges in a row will work well as long as they all calibrate the same. The problem with this is that very inexpensive gauges often do not read the same and there is no way to correct for this.
Brian
Since I have three multicylindar bikes I might as well invest in a tool I will be happy with.
Looks like the Carbtune and TwinMax are both good (non fluid, hard to F' up) options although I don't fully understand how the Twin Max works and especially how it will get the job done on the C14 with the center adjusting procedure as spelled out in the manual.
As for the motion pro tool, when I turn the calibrating screws they feel very unsmooth. I suspect poor workmanship.
