Interesting statement considering those Carbs have just like Webers, Dellorto's and Solexes Main jets, Idle Jets, Air Correctors, Needle Jets (Emulsion Tubes) and the Air Corrector's are High speed and low speed (Weber low speed air correction is built into the idle jet with differing F numbers designating the air correction hole size).

In fact they have as many Jets as the others and add a couple more options such as Needle tapers and lengths, Multiple tapers and as well Slide cutaways to add into the mix when tuning.

CV Vacuum Carbs also add into the mix different spring lengths and rates to boot, So they are not actually any simpler.

The Biggest difference is that besides picking a size with Webers etc such as 40mm, 45mm or the rarer 42mm, 48, or 50mm and 55mm base sizes you then can alter Main and Auxiliary Chokes or venturi's to fine tune to the engine characteristics.

With Bike carbs whilst good you must make sure you get the right size to suit from the beginning as there is no way of changing Choke sizes other than a new set of different carbies.

So in truth there are pro's and con's to both approaches and if you know what you are doing both types can be jetted to work, If you do not know then both can and will be problematical to make work right.

Therefore just because you lucked out with a set of bike carbs that worked OK with your particular setup does not mean everyone else will be as lucky unless they do some serious research before jumping in and that applies to all carbs, Car specific or Bike specific.

There are also many different non interchangeable Mikuni and Keihin jets to be aware of with different variations of carbs.

With the FCR Bike carbs there is also a very real problem that can cost you an engine they run what is called a Vacuum plate on the slide and the stock ones have a releif on both sides and they break off a couple of sections of these plates after a while, There are billet replacements relieved on one side only that are better but the vaacuum plate is a weakness in the design to be aware of and check on a regular basis.

Not so bad on a race car but a pain in the Posterior for a road driven vehicle to check for cracks on a regular basis, I see them break more often on single cylinders with stronger vacuum pulses but they do also break on four cylinder engines.