TWO-STROKE TUESDAY: WE RIDE THE LAST FACTORY 125

This archived test was originally printed in the July 2005 issue of MXA.

You didn’t even have to attend an AMA Supercross to know the brand and rider of the loudest bike on the track. You could hear it by driving past the stadium in your car. Now, you might wonder how it would be possible to tell the model and rider from the freeway. That’s simple–it only requires three jumps in logic: (1) The loudest bike was a 125 two-stroke. That was easily discernible by the high-rpm whine of the engine as its sound rose from the midst of a bunch of four-stroke washing machines. (2) The only factory-backed 125 two-stroke on the circuit is a Yamaha of Troy YZ125. (3) Australian Brett Metcalfe is the sole surviving 125 two-stroke rider in Supercross. He is a lonely man when it comes time to borrow a plug.

Thus, without looking up from your steering wheel or your race program, you could tell when Brett Metcalfe went by. Amazingly, even though everyone winced at the sound of Metcalfe’s YZ125, his bike barely registered 95db on the AMA sound meter (the four-strokes were pushing 102db). Why did Metcalfe’s bike sound so loud, if it was so quiet? First, its tone was unique. It was one of a kind. Second, the AMA sound test is a joke. The results vary from week to week on the same bike, and two-strokes, because of their power valves, slide under the AMA’s prescribed rpm settings.

SINCE EVERY OTHER FACTORY-SPONSORED RIDER ON THE AMA CIRCUIT IS ON A FOUR-STROKE, WHO DID BRETT METCALFE MAKE ANGRY? WHY IS HE THE LAST OF THE MOHICANS?

WITHIN A LAP OF RIDING METCALFE’S BIKE IT BECAME READILY APPARENT JUST WHAT THAT 22 POUNDS MEANS ON THE TRACK. THERE WASN’T AN INSIDE LINE WE COULDN’T HIT. 

Wanting it was the easy part, actually getting Metcalfe’s YoT machine was more difficult. YoT team manager Dave Osterman liked the idea–after all it wasn’t like Yamaha of Troy was setting the world on fire. A little publicity might pay off a few disgruntled sponsors. But, Dave had to get approval from Team Yamaha before he could hand Metcalfe’s bike over to MXA. We waited for the official word…and waited. We were patient…at first. Then we decided to go over the heads of Yamaha Racing and pitch our idea to Yamaha’s corporate marketing division. They were the ones faced with the burden of selling 125 two-strokes in a four-stroke world. We thought they might be more responsive to our request. Three days later we had our hands on Brett Metcalfe’s YZ125 (and very few friends at Yamaha).

So what’s the first thing we noticed about Brett’s YZ125? The weight. That’s because the first thing we did was put it on a scale. Tipping the scales at the AMA limit of 194 pounds, the YoT YZ125 is a feather in a brick world. It was light on the scale and light to the touch. Considering that most 250F’s weigh 216 pounds, Metcalfe’s YZ125 is in a world of its own. Within a lap of riding Metcalfe’s bike it became readily apparent just what that 22 pounds means on the track. There wasn’t an inside line we couldn’t hit or a jump we couldn’t whip the YZ125 off of. This is the biggest advantage Metcalfe’s YZ125 has over the 250Fs.

There is a misconception out there that 125cc two-strokes don’t make as much horsepower as a 250cc four-stroke. Not true. On the dyno there isn’t a gnat’s hair difference. It isn’t horsepower that puts a 125 two-stroke at a disadvantage. Since the AMA allows four-strokes to have twice the displacement, they are able to turn that bonus into tons of torque. Four-strokes produce very broad powerbands and lots of torque–which means that they are making good power at 5000 rpm and good power at 13,000. A two-stroke engine works like the shutter of a camera–it only makes good power when the shutter is open (normally between 10,000 to 12,500 rpm).

THE AMA GAS RULE WAS A WASTE OF PAPER–AND MORE THAN ANYTHING HASTEN THE DEMISE OF 125 TWO-STROKES. WHO KILLED THE 125 TWO-STROKE? SOME GENIUS AT THE AMA.

The second suppressor on two-stroke prowess is the AMA’s stupid unleaded gas rule. Passed in 2004, this rule killed high compression, high rpm two-strokes, but didn’t have any effect on four-strokes. The AMA gas rule was a waste of paper–and, more than anything, hastened the demise of 125 two-strokes. Who killed the 125 two-stroke? Some genius at the AMA.

All that said, We were impressed with the overall power out of the Yamaha YZ125. The boys over at Yamaha of Troy have built Metcalfe’s YZ125 into a mid-and-up monster. Even in the deepest berms, all you have to do is fan the clutch and you’re rewarded with an explosive surge forward. That surge doesn’t end quickly as Metcalfe’s bike revs beyond the normal 12,500 rpm (his bike runs $40 a gallon VP Pro2 gas to defeat the AMA unleaded rule). This is a really good 125 engine.