Imagine a 3 inch dia. pipe 4 ft long. Cap both ends and then apply a low pressure (vacuum) source to one end, in some amount of time, the internals of the pipe will equalize pressure everywhere inside the pipe until it equals the vacuum applied to it. (Assumes the pipe will not collapse from intense pressure.)
Now put a pin hole in the opposite end of the pipe from the vacuum source. The pin hole will begin to equalize pressure on both sides of it until they are equal. If one maintains the low pressure source at one end, it will establish a flow of material completely dependent on the viscosity of the fluid, the size of the orifice, and the pressure differential across the orifice. A large orifice will equalize pressure faster than a small orifice, assuming we hold the vacuum source constant, the supply pressure constant, and don't change the viscosity of the fluid to and from the pipe. See also:
http://forums.sohc4.net/index.php?topic=83904.msg945765#msg945765This is the physics explained. For the CB500, the vacuum source is the engine cylinder, the fluid is the air ingested and any change in the cross sectional area of the inlet duct is an orifice.
To limit he increasing speeds and HP from engines, NASCAR mandated a restrictor plate inserted in the inlet duct path. Using well-know orifice technology this effectively limited the engine output capability on all the normally aspirated engines allowed in the race, and the top speeds of the cars all plateaued.
To suggest that the inlet restrictor has no effect on how the engine runs, defies the laws of physics. And, any testing that "proves" otherwise must be technically flawed or intentionally misleading, imo.
I further maintain that there is
something different about 649 carbs internally, from the 627 carbs beyond the main jet size and needle position and idle setting, to allow it to operate with that restrictor plate. Which is why simply changing jets/adjustment in 649s and removing the restrictor inlet does work the same as using 627 and no inlet restrictor. I fully expect that using jets and settings for the 627 carb would result in failure, as well.
If trust is an issue, I don't trust any test results on models with 649 carbs, as being in any way applicable to users of the 627 carb. At least until it is known exactly what the difference is between the two set up types. I don't have access to 649 carbs to check them myself, as they are mostly irrelevant to Cb500 users in most locales in world.
If you are happy with your variant, fine by me. Just don't tell me that adjustments are the same for all. The physics simply do not support it, regardless of what popular opinion agrees upon. Next we will learn that the speed of light is different in Germany, Holland, Swiss, Italy and probably Austria, from what the rest of the world experiences. /jk
It occurs to me that "where mandated" and "where sold" may be two different issues, and may have been a methodology used by Honda to market a specific model in more than just one small marketplace. For example, let's say you wanted to sell into the Swiss marketplace that has special importation requirements, but the low production number don't make economic sense for a model only sold there. If you could market the same machine in several other market outlets, the economics of volume purchases could make this feasible rather than ignore completely the small market that has a demand for something slightly different from your main production model that it sold everywhere in the world.
I do know that there is a county that requires special licensing based upon engine displacement, with the break point at 500cc. Ergo, we have a CB500 K3 and a Cb550 K3, same bikes, different displacement. However, I expect that the CB500 K3 was sold into more that just the countries that had that 500cc break point written into law.
Oh well. We get to do whatever we want to our machines. Doesn't matter if it makes sense or not.
