Mike - Pat's got it right. Its all a matter of emissions standards. Under the Clean Air Act Amendments of 1990, Congress (and the President) required that emission standards of all types be clamped down. On the mobile sources side (i.e., anything that moves), EPA started with the largest population first - passenger cars and light trucks. The emission standards for automobiles starting going down in the early 1990's with onboard diagnostic systems required as part of that decline in allowable emissions. OBDII came out in 1996 which was a more sophisticated computer system that monitored every aspect of emissions related performance in motor vehicles. Heavy trucks emissions are following the same path as are motorcycles. Naturally, marine engines could not escape more stringent standards if everything else was being regulated. Accordingly, the marine rule requires manufacturers to produce engines that meet lower emission levels phased-in from 1998 through to 2006 with the last year being the most stringent for emissions of oxides of nitrogen and hydrocarbons.
Nothing in the regulations bans any particularly technology. For example, Bombardier believes it has developed a two-stroke engine in the Evinrude E-tec line that will meet EPA emission standards for a long time to come. Accordingly, they are still manufacturing and selling a two-stroke. Other manufacturers could also invest in the R&D to figure out how to make two-strokes compliant with applicable emission standards - or they could go with four-strokes. For most manufacturers, its a matter of whether to invest the R&D dollars into improving two-strokes emission performance or working with four-strokes known to be fairly clean already. A good summary of the EPA requirements is available at http://www.epa.gov/otaq/marinesi.htm.
The People's Republic of California is a whole other story. Since California had vehicle emission regulations pre-dating the Clean Air Act, California was given a "waiver" so that their program could operate "in lieu of" the federal program. Other states can choose to adopt California's standards or stick with the federal. That's why states like NY, NJ, VT, and Massachusetts have more stringent emission standards for cars. If that's not confusing enough, California is trying to implement mandatory carbon dioxide emission limits for automobiles, along with the Northeast and Northwest states. The auto manufacturers have sued since the only way to regulate CO2 from cars is to ratchet down fuel economy to levels not possible with existing (or developing) technology. Besides, fuel economy is regulated solely by the feds without any waivers for states.
Hope this helps a bit more.
JC
