THE ULTIMATE YAMAHA YZ125: SMUGGLED IN FROM AMSTERDAM BY MXA

BY DENNIS STAPLETON

I’m never disappointed when I am riding a Yamaha YZ125, and there is good reason for that. It is the best bike to be tapped out on—flat-out hauling with the engine at full shriek and my brain overdosing on endorphins. It is like a dream world—you know, the dream that every motocrosser has the night before a race. The one where you are shifting through the gears like a TV remote that accidentally hit on a cooking show. In this dream, you don’t need a throttle, because there is only one setting that a dreamer uses—wide open, locked wrist and disconnected brain. I love that dream, but the truth is that I could go out on my KTM 450SXF with 100 hours on the engine and tool around the track in second gear and beat my dream lap time by 10 seconds. I hate it when reality rears its ugly head.

With the 2020 World Two-Stroke Championship scheduled on October 10, the MXA wrecking crew started discussing who gets to ride which bike. The World Two-Stroke Championship is held at Glen Helen, and there is not a single MXA test rider who wants to tackle Mt. Saint Helen while straddling a stock YZ125’s measly 33.52 horsepower.

Oh, make no mistake about it, one MXA test rider is going to find himself looking down the blue snout of a Yamaha YZ125 with a 70-mph start straight staring him in the face. After the start comes a steep hill that climbs 20 stories before plunging downhill, only to face an even taller 22-story uphill midway through the first lap. Whatever bravery you showed on the way to the first turn will be instantly erased at the first hill, as more powerful bikes dance away on the brutal climb.

So, while most of the MXA crew tried to finagle a way to get a seat on a 250SX, YZ250, TC125, FX300, XC300, TC250 or TM 300MX, Daryl Ecklund decided to do something about the YZ125 dilemma. It turns out that Yamaha of Europe sells a GYTR YZ125 high-performance engine kit. Think of it as the 125cc equivalent of KTM’s 300cc upgrade kit for the 250SX. The complete GYTR kit comes with an adjustable combustion-chamber cylinder head, a ported cylinder, special power valves, a high-performance ECU black box, stiffer clutch springs, a carbon fiber ignition cover, VForce reed assembly, increased inertia magneto rotor, a GYTR pipe and silencer, and two pistons.

This is the engine package that Yamaha’s sponsored riders use in European EMX 125 and the Yamaha Cup 125 races. Sounds great, doesn’t it? Well it is, if your name is Maxime, Rene, Alberto, Giuseppe or Matteo. The problem for every Tom, Dick and Harry from Cleveland is that Yamaha does not sell the GYTR YZ125 high-performance engine kit in America.

Even an influential guy like Daryl Ecklund, a former National Pro, MXA managing editor and industry insider, couldn’t get Yamaha USA to get him a GYTR YZ125 kit. But, Daryl travels extensively in Europe, and he knew a guy, who knew a guy, who knew a girl who was dating the guy who worked in the Dutch warehouse where the GYTR YZ125 high-performance engine kits are stored. A month later, an unmarked box arrived via FedEx. Inside was the clandestine GYTR YZ125 kit that was smuggled out of Europe.

And that is where I come in. It turns out that Daryl had no intention of racing a YZ125 at the World Two-Stroke Championship. He just doesn’t like to be told that he can’t have something that he wants. So, he got a GYTR YZ125 kit, which he immediately handed over to me. And this is the story of how the MXA wrecking crew built the ultimate 2020 Yamaha YZ125—at least within the contiguous United States.

The first thing I did before wasting a lot of time rebuilding every aspect of our well-used test YZ125 was to run it on the dyno. It made 33.52 horsepower, with the peak at 11,500 rpm. Once the base runs were done, we took the stock parts off the YZ125, put the GYTR YZ125 high-performance engine kit on and put it back on the same dyno one hour later. It pumped out 36.77 horsepower at 11,400 rpm. Just to make sure that everything was spot-on, we showed the GYTR dyno chart to Mitch Payton. He was impressed by the 3.25-horsepower increase, but furrowed his brow when he saw that the GYTR kit signed off immediately after hitting its peak. “Take it apart again and check everything before putting it back together. There is no over-rev, and it falls off the pipe so fast that you’ll never get anywhere without shifting like crazy,” he said. So, apart it came. We measured everything and checked the power-valve settings, the tolerances and the electrical fittings. Back on the dyno, it ran the same. It was puzzling. 

Mitch called Jody to see what he wanted to do, and Jody said, “Take off the GYTR pipe and silencer, put on the Pro Circuit YZ125 pipe that Ryan Villopoto runs and dyno it again.” Suddenly, the GYTR high-performance engine kit was making 37.34 horsepower at 11,700 rpm with acceptable over-rev. The GYTR kit pipe’s only identifying stamp said “GYTR.” It was obviously made by an outside vendor, but it was not a good pipe.

POST-TEST NOTE FROM EUROPE: After MXA published our test of the GYTR Yamaha YZ125 kit, we got a letter from Yamaha of Europe apologizing for the exhaust pipe issues. They said that “In some GYTR kits we had the wrong exhaust pipe, which influenced the kit in a bad way and every customer who got wrong pipe will get a new one free of charge.”

MXA appreciated the European’s quick response, although it came after the test had been published and put on the cover of the June 2020 issue.

The man in charge of the GYTR project at Yamaha Motor Europe said that the 2020 GYTR YZ125 kits are now “offered with the latest improved spec of the GYTR pipe along with an improved CDI to have the latest specifications. GYTR’s goal is to keep on updating and improving/ innovating the GYTR two-stroke kits every year. Overall test is really nicely written and has awesome pictures. Well done. Really a pity that we shipped the wrong pipe for the kit.”

With the Pro Circuit pipe and silencer combo, the YZ125 engine was making almost 4 horsepower more than the stocker at peak. Now I could confidently go about changing the rest of the 2020 Yamaha YZ125 to suit the demands of the World Two-Stroke Championship.

I had no real concerns about the vast majority of the YZ125 package. It was all good, but I did change the stock bars to ODI KTM-bend handlebars (with soft ODI glue-on grips) and put on a high-pressure CV4 radiator cap. I also added heat strips to try to keep an eye on the high-rpm engine. I switched out the stock air filter for a Twin Air and changed the fluids (transmission and brakes) to Maxima. In stock trim, the YZ125 comes with old-school Dunlop MX52 tires. I put on the Jeremy McGrath-designed Maxxis MX-ST tires, and was brave enough to replace the stock 100-width rear with a 110-width tire. I felt that the added horses could pull it, and the bigger size would lessen the chance of flats on the brutal Glen Helen layout. DeCal Works did the graphics and seat cover to make the YZ125 look pretty.

All that was left was the suspension. We love the stock Kayaba SSS components, but they are too soft for a Pro to bomb down Mt. Saint Helen on. We’ve had great luck with WP Cone Valve forks on our Honda CRF450, Suzuki RM-Z450, KX450, and all manner of Husqvarnas and KTMs. And, in truth, WP XACT Cone Valve forks are what Showa A-Kit forks were 20 years ago—the best factory fork available over the counter at a semi-reasonable price.

WP wanted to know who was going to race the bike, and I told them Josh Mosiman, because his weight was close to mid-way between all of the MXA test riders— split equally above and below each half. On the track, the Cone Valve coil spring forks had a nice crust that held them up in the choppy stuff. The suspension would break free when hitting big bumps and jumps. They offered excellent control and commendable bottoming resistance. We gave up some of the comfort of the Kayaba SSS rear shock, but overall the WP fork and shock had less of a pitching motion, which kept the bike in a more balanced position for racing.

Of course, it seemed like blasphemy to take Kayaba SSS suspension off for WP components, but Cone Valve spring forks are top-of-the-line. The stock YZ125 forks are very good, but they are set-up for an average 140-pound Novice rider—not a Pro facing some of the biggest, gnarliest, square-edge bumps in the sport.

As for the engine, it not only made beaucoup horsepower and torque, but we were able to take the stock engine components off and set them on a shelf to use again in a pinch. Now, I just gotta find a test rider to race it; the 4 extra horsepower should seal the deal.