Europe was dealing with emissions long before California.
While that was going on CARB was invented, and "laid" Tier i & Tier II regs.
EPA followed in CARB's footsteps, then stepped out with Phase I & Phase II regs.
Europe's 2008 regs will become the world's (civilized) most stringent standards. But only after the good 'ole USA did all the work, and enforcement.
CARB commonly referred to in the Firearms industry as
'Wackafornia', has again reared it's ugly head with new regs that will cost the OPE Industry one billion dollars ($1,000,000,000).
It claims that the vaporization, and permeation (leaking thru fuel lines, gaskets, and containers) was-is worse that emitted combustion (muffler exhaust).
Go figure that one out. If it's worse....why did they fight about other things earlier, and keep the good stuff to last....??????
Regarding Limiter Caps & 'break in', a new engine will pollute more prior to breakin, not the reverse. More THC's are emitted.
As the engine breaks in, it becomes more efficient.
The limiter caps are mainly designed to function as Stihl Tech commented about electronics, which is to keep the engine operating within better emissions, and operating ranges, not solely for anti-leaning.
Engines that are on the lean edge can produce speed, but the component service life is greatly reduced, and when that happens engines run much less efficiently.......quicker death.