The operation of a CV carb at varying altitudes is one of those "yes and no" types of situations. In the strict physics based reality, it does not adjust jetting or fuel delivery to the engine. It does, however, affect...usually positively...throttle response to a large degree...not for performance but for a better fuel delivery. As you climb in altitude with jetting numbers that are optimum for low elevation, power tends to drop as available air density drops. Regardless of the carb design, a rider tends to apply more throttle as a result, and the bike starts running richer and richer, sometimes even chuffing black, rich, visible exhaust. The CV carb design only allows the slide to operate in response to air flow which in turn gets limited by reduced combustion efficiency. So, even though the rider is twisting on the throttle to try to produce more power at high altitude, the diaphram is limiting slide movement in a more efficient manner in those extreme conditions compared to a straight cable-pull or linkage slide. While the straight cable-pull/linkage carb can perform just as efficiently as the CV carb in those extreme altitude situations, it takes a lot of precise throttle control on the part of the rider.
The reality is that a CV carb needs proper jetting for altitude extremes for good performance. When I was still running the CVK34 on my KLX300, it needed rejetting to the leaner side of the spectrum when I went from my home elevation of 1700' to consistent rocky mountain levels of 7000' and above. It usually wasn't really noticeable with my home jetting until somewhere after about 9000'. Now, my KLR650's that I owned didn't require rejetting, but that was only because they had a little more power/torque to sacrifice. My KLX got absolutely anemic at 10,000', requiring constant up-and-down shifting to make forward progress. With a proper rejet, performance was way more crisp and responsive without all the rowing on the shifter.
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