This past decade saw much change and technological advances compared to the 1990’s. The Pro National scene went from 99.9% of the e bike damen being two-stroke (Yamaha’s YZ400 was about the only thumper out there in the late 90’s). 2001 was the beginning of the end for the 125 2-stroke because of the YZ250F, and soon after the other companies followed suite. By 2006 the scenario had done a complete 180. Within the past 10 years, there have been some atrociously made bikes, as well as the best bikes ever made. This list may not include the entire globe, but should cover the United States, along with many other countries that have similar inventory of bikes. My list is objective and unbiased; I am going by which bikes are being sought after and bought the most, both new and used.
Yamaha is the only Japanese manufacturer that still imports two-stroke motocross bikes to the U.S.. They have had together the entire time, but the YZ250’s best years are 2005 and newer. The lightweight aluminum frame and updated suspension (2006) makes the bike nimble, quick, and easier to ride. Power right out the box is excellent for almost any amateur, so there really isn’t a whole lot you need to do to do for it to be competitive, other than a suspension re-valve for your weight and riding style. The YZ250 has quite a bit of bottom-end power for a 2-stroke, and has plenty up top. You can move the power-band around with an aftermarket pipe if you don’t like the stock curve. Probably the best modification for engine performance is porting. It’s relatively cheap, and if you get it done by the right person this bike will absolutely rip.
I know I said that four-strokes have dominated the pro motocross and supercross scene the past several years, but that doesn’t mean people don’t buy two-strokes anymore. In fact, riders are realizing how expensive four-stroke motocross bikes can be if there is a major failure, so they’re moving back (or to) two-strokes. Don’t fool yourself, the 125 two-stroke is a very fast bike, even stock, when properly tuned. When James Stewart entered the pro-scene on a 125, his lap-times were often as fast or faster than a lot of the 250cc riders because he knew how to ride his KX125 so well. He continued to beat four-strokes in 2004 when 250F’s started becoming “the bike” to race, so you know the bikes wasn’t lacking, that much.
The Yamaha YZ125 has reigned has “the bike” to get in the 125cc-class for many years now. It may not have the best of everything, but as an overall package it’s arguably one of the best motocross bikes ever because it is versatile. Although, the motor hasn’t changed much since 2001, and the chassis/suspension since 2006, there really isn’t a whole you need to do to this bike to race it.
Unlike most other 125’s, the YZ125 has some bottom-end power. So if you’re not afraid to finger the clutch a little, you can turn it into a woods weapon because it is so light. The center of gravity is lower than four-strokes, adding to its maneuverability. I like riding both two- and four-stroke dirt bikes, but getting on the pipe and ripping it up on a YZ125 is just too much fun!
This bike also makes my top 5 list because of how easy maintenance is, as well how cheap it is to repair if something major happens because of less moving parts. A four-stroke engine costs 3-4 times as much if something catastrophic happens, especially if you have a shop do the work. On a two-stroke, as long as you change the oil regularly, a top-end kit (usually just a piston, rings, gaskets, etc.) costs around $100-150. Even if your cylinder gets scored you can re-plate it to new condition for about $200.
You guessed it, another Yamaha. Not only are its two-strokes good, but so are the four-strokes. The first year of the YZ450F was 2003 (superseding the YZ426F). This is when the bike was titled “Impossible To Ride.” It did have a lot of torque just because it’s a 450, but the top-end power was unbelievable. It was hard to hang on to the bars for less-experienced riders (Here I’m thinking, “supermoto, supermoto….”). Well, it is a little harder to ride than most others in its class, but any 450cc motocross bike is going to have a lot of power if it’s fresh. Don’t let all the “internet hype” get to you, it was still a great bike. In fact, some say it had the best 450cc from 2003-2005.
The second generation YZ450F got even better (for the most part) in 2006 with the all-new aluminum frame. This reduced weight and helped with handling (more on that in a little bit). The power curve was changed considerably, changing from a top-end monster to a more mellow beast. Some complained, others loved it. Don’t worry, the engine is probably the easiest to change, it just takes a little dough.
Moving on to other things, the YZ450F’s suspension is good in stock form. Just make sure it has the correct spring rates for your weight and riding style. The handing on this bike is said to be an issue. Supposedly the steel frame was to blame and made it feel heavy and turn slower. I mentioned that 2006 is when Yamaha switched to aluminum frames for its four-stroke motocross bikes, and doing this resulted in better turning and handling for this bike. 2010 is really when handling was a positive for the YZ450F with the new bilateral-beam frame and centralized weight. It made it feel more like a two-stroke, but not quite because of its weight.