Hmm, I think that the Twinmax can actually be quite sensitive, in theory at least. But, since it is a differential pressure
transducer, it is only good at giving you relative readings between 2 carbs, whereas the absolute readings may be quite high
(or quite low).... so if both carbs are waaaaaaay out of wack as far as flow rates go (either one extreme or another) but are
still relatively close together then it could be a very frustrating process to try to figure out.
I ended up getting a 4-channel Morgan CarbTune 2 (now called the Pro model) and am quite happy with it. I bought it from the
mfgr across the pond in Britain, but there are some US distributors for it. It is actually more of a rotameter than a manometer
(uses stainless steel slides in glass tubes) but works well on the bikes I have tried it on so far (4 Cylinder Kawasaki Concours/GTR1000, and Tillie, my R65LS). Using it I can get my KAwasaki's carbs set to be all within about 1cm of Hg pressure, total spread.
It essentially has (2) dynamic ranges - using it right side up gives you absolute values according to the scale and it is quite sensitive, though following the directions to put small dampening orifi in the vacuum tubes provided just the right amount of dampening so the slides weren't bouncing around too wildly for practical use. The classic airheads with Bing CVs have much lower vacuum pressure to work with, so you turn the thing upside down (don't try that with
liquid gauges !!!!) and it essentially provides a full scale reading that is approximately 20% of the "normal" full scale reading. In this mode I can get Tillie's carbs dialed in quite well.
I am sure that there are other products out there, but I have been quite pleased with my CarbTune and expect that it will last a long time.
