MX Boy 100: No it's not emmissions. EPA has no current plan to enforce any restrictions on CLOSED COURSE machinery. The FIM adopted the unleaded fuel rule so they could have races in several European countries. Back when Clear Channel went behind the AMA's back to the FIM for the 2003 Supercross rights they struck a deal. (It was ALL about money, AMA wanted more, Clear Channel wanted more, their egos got too big for each other) So when the AMA and CC finally reconciled, the FIM wouldn't let their deal go. So the World Supercross GP was born. Basically it's the AMA Supercross championship with two or three European rounds attached to it like a wart. The FIM was being difficult, and the AMA decided to give into the unleaded fuel rule (which the FIM had no real reason to do, just to try and show that they were the pitcher, and the AMA the catcher; politics in other words). Leaded fuel has no real environmental issues compared to unleaded in MOTOCROSS. Performance is a different story, as four-strokes lose 1-2% power, and two-strokes lose a whopping 7-8%. Which bikes suffer the worst? 125cc two-strokes due to the fact their already underpowered. VP Racing's Bruce Hendel says "The U.S. is given an exemption on the use of leaded fuels for competition, so there wasn't a governmental or legal reason to switch. It was purely political. From an enviromental standpoint, unless you're using catalytic converters, there's absolutely no difference." (And no, MX bikes don't use catalytic converters) Now you may be saying "So there's just a power decrease.", oh but you're wrong. The primary reason lead is used is because it's a cheap was to improve octane. The higher the octane, the hotter an engine can run so the fuel doesn't detonate prematurely (pinging). Unleaded fuels can be made to have the same octane, but with one caveat. While 108 octane leaded race fuel might cost $8 a gallon (wow, some expensive stuff, right?), unleaded fuel with the same octane costs (are you ready?) in excess of $40 a gallon, no typo. See how this hurts the privateer two-stroke rider? He must switch to a basically stock bike, because a fully modified race bike needs high octane. Out of the stock bikes four-strokes are better (well at least in the 125 class). So I will repeat, unleaded fuel means death for two-strokes. If you only race locally have no fear, this only applies to AMA pro races. But if more and more pros stop riding two-strokes then the manufactures are going to stop developing new technology for them, and it won't be long before the two-stroke is a thing of the past. And I will cry, because even if four-strokes are better, I love to hear two-strokes, and the smell of premix.