No, the CDI unit from a Honda VFR 400 NC24 will not work on an NC21. While both models share the same engine size and basic layout, there are significant differences in the electrical systems between the two bikes. The NC24 uses a different ignition system than the NC21, and the CDI unit is not interchangeable.
If you are looking to replace the CDI unit on your NC21, you will need to find a unit that is specifically designed for that model. You can find replacement CDI units from a variety of sources, including online retailers and motorcycle salvage yards.
