How does the VTEC system in Honda VFR800 Interceptors, 2002 and newer,
work?  I know the engine switches from two to four valves per cylinder
at 7000 rpm.  What I would like to know is the mechanism by which this
change is accomplished.

Thanks.

Hello racecar,
I was not familiar with this technology either and I thank you for
getting me interested. I have found information which explains it to
me and hopefully  will you also. The first article relates to
automotive applications, but is good for a starter. The second article
relates specifically to the Interceptor.

http://www.canadiandriver.com/articles/jk/at_011205.htm
Honda technology is always at the cutting edge: designed, refined,
implemented, and produced to perfection. The latest Honda technology
to hit the streets is actually an improvement on their VTEC (Variable
valve Timing and lift Electronic Control) engine technology. They call
it i-VTEC (the i is for intelligent) and Honda presented it to the
Technology panel of the Automobile Journalists Association of Canada
at their annual Car of the Year testing as a candidate for the year's
"Best New Technology".

http://www.sportrider.com/bikes/146_0204_int_vtec/
In the mid-1980s, the Honda CBR400F (not sold in America) utilized a
DOHC-VTEC system similar to that used on the cars. Back then, it was
called REV (Revolution Modulated Valve Control) and the setup
incorporated split rocker arms to work eight of the engine's 16 valves
below 8500 rpm, and all of them above that. The trouble with grafting
these automotive-style VTECs on a bike like the VFR is that bikes have
long since outgrown rockers, and the size penalty for extra lobes
would be too great given Honda's goals for the 2002 Interceptor. Hence
a further enhancement called Hyper-VTEC. First utilized on the
Japan-market CB400 Super Four, and now the Interceptor, Hyper-VTEC
retains the top end's basic layout of DOHC with direct-actuation (no
rockers or lifters), and two of each cylinder's four valves operate as
before. The other two, a cater-cornered intake and exhaust pair,
incorporate a small pin inside the bucket which operates under
hydraulic pressure. At high rpm, the pin acts as an extension of the
valve stem itself and the valve works exactly as normal. At lower rpm,
the pin extracts, and the bucket pushes on the empty space-leaving the
valve closed.
Similar to the automotive VTEC, the VFR's system is controlled by
electronics and hydraulics. At the crossover point of 7000 rpm, an
electric solenoid activates, allowing oil pressure to build in the
cavity housing the pin. The pin is then pressed into place (in 15-20
milliseconds) between the bucket and valve. Honda anticipates that,
because the VTEC valves are not under constant operation, they require
adjustment less often than the non-VTEC valves. As a result, no shims
are incorporated, but rather buckets with varying thickness, and this
reduces reciprocating mass as well as noise. As you would expect,
Hyper-VTEC also allows for more aggressive cam timing, and the VFR's
cams benefit from more duration (7 degrees intake, 3 degrees exhaust)
and overlap (12 degrees) compared to the previous model.

I have only shown a small part of the articles here. You should should
look at each one as there is much more interesting info and drawings.

Thanks, Redhoss

The link with the diagrams was exactly what I was looking for.  Thanks.