MXA TEST: WE RIDE PRO CIRCUIT’S FULL-RACE YZ250F

TO TELL THE TRUTH, MOST MXA TEST RIDERS PREFER TO TEST BOX-STOCK SHOWROOM BIKES. IT IS GOOD WORK FOR A GOOD CAUSE.

The MXA wrecking crew tests all kinds of motorcyclesevery displacement, brand and style. Occasionally, our test bikes are factory-built works bikes. Sometimes, the bikes are the modified concoctions of the privateer teams. Often, they are heavily modified production bikes. But, more than likely, they are plain old stock production bikes. To tell the truth, most MXA test riders prefer to test box-stock showroom bikes. Why? MXA believes that telling the public all the ins-and-outs of a production bike helps local racers make an informed buying decision. It is good work for a good cause. Works bikes, AMA National bikes and exotic project bikes are a blast, but they don’t have the grassroots connection of an off-the-showroom-floor machine. We are well aware that the vast majority of motorcycle buyers don’t get the opportunity to ride every bike made and discover its flaws, or work out fixes for its flaws, before plunking down their cash.

 WE LOVE TO FIND SIMPLE,  INEXPENSIVE, DO-IT-YOURSELF FIXES, BUT AT SOME POINT
WE HAVE TO THROW FINANCIAL RESPONSIBILITY OUT THE WINDOW.

That’s why we spend countless hours coming up with solutions to the problems that plague most production bikes. We feel good when we solve problems, especially when our solutions become de rigueur throughout the world. To us, it is a crusade, First, we resolve the simple problems. Then, we start looking deeper. We love to find simple, inexpensive, do-it-yourself fixes, but at some point we have to throw financial responsibility out the window and go searching for the best of everything. The search for the perfect fix can be difficult, but sometimes we are lucky and the fix comes looking for us.

A FEW DAYS BEFORE WE WERE GOING TO TEAR OUR YZ250F DOWN, IT GAGGED ON A VALVE AND EXPELLED COPIOUS AMOUNTS OF FRAGMENTS.

This was the case with MXA’s 2006 Yamaha YZ250F. We have been testing, racing and working on the YZ250F since last summer. We put the bike through the ringer and were on the verge of taking the bike to the final level with a full-blown overhaul. But as fate would have it, we were one race too late. A few days before we were going to tear our YZ250F down, it gagged on an intake valve and expelled copious amounts of expensive aluminum fragments. Oops!

We put Yamaha’s Engineering Department on the case (which eventually resulted in Yamaha’s recall of all 2006 YZ250F valves) but, in the meantime, Pro Circuit’s Mitch Payton called and said that he was interested in building a full-race YZ250F version of his Monster Energy KX250F and Sobe/Samsung CRF250. He wanted to know if we would do the test cycles on the complete engine kit. Mitch committed to provide all the parts, the know-how, dyno time, mechanical work, race shop expertise and a brand-new Yamaha YZ250F?except for the wheels. Say what? Believe it or not, Mitch had a brand-spanking-new YZ250F, but somehow in the shuffle the wheels had been procured by a Pro Circuit support team. We told him that it wouldn’t be a problem, and placed a quick call to  White Brothers’ Braden Dahl. White Brothers import and lace Talon hubs. They put a set of Yamaha-blue Talon wheels on a UPS truck a day later.

Of all the hop-up shops that the MXA wrecking crew works with, Pro Circuit is the most professional. If Mitch says something is going to happenit does. Pro Circuit handled every single detail of our test YZ250F. The triple clamps, clutch perch/lever, throttle tube, foot pegs, exhaust system, graphics, holeshot device, front brake cable guide, fork valving, shock valving, titanium shock spring, clutch cover, ignition, titanium valves, piston and valve springs came directly from their Corona, California, hot house. And the list of parts that weren’t from Pro Circuit was rather short: Hinson clutch, Talon hubs, Lightspeed carbon fiber (skid plate, case guard and chain guide) and Renthal sprockets, handlebars and grips.

Once we were through ogling the Pro Circuit catalog that was our new YZ250F, it was time to hit the track. Pro Circuit leaves nothing to chance, and although they handed us the bike for a long-term test, they sent suspension guru Bones Bacon and National mechanic Kevin Strikwerda along to babysit the bike on day one.

NOW YOU MIGHT THINK THAT A HAND-BUILT BIKE, WITH TEN GRAND WORTH OF MODS, MUST BE AWESOME TO RIDE FOR THE FIRST TIME. WRONG.
 
Now you might think that a hand-built bike, with ten grand worth of mods, must be awesome to ride for the first time. Wrong. It was terrible. On the first few break-in laps (break-in for the test riders, because the bike had been dynoed more than a few times during its buildup), we couldn’t get the YZ250F to settle down and get comfortable. This wasn’t what Bones wanted to hear, but he went back to the basics and checked the sag. It was 110mm. Yamahas don’t like their sag set over 100mm. Instead of touching a single clicker, Bones reset the sag at 97mm and sent us back out. What a difference 13mm makes. It was as if we were riding a completely different machine. The rear wheel tracked with the front instead of kicking side-to-side off every bump. Having the rear ride higher also helped put more load on the front forks, which were still too stiff (even with the increased load).

After trying a few clicker settings on the forks, Bones decided to take 10cc of oil out of each fork leg. Again, the change was significant. The forks went from being too stiff to really soft. Back to Bones. We tried stiffer clicker settings. No dice. Bones added 5cc back into each fork and sent us back out. We’d found the sweet spot through trial and error.

For the first few hours, we were so focused on the suspension settings that we didn’t really pay much attention to how the engine was running. However, the engine mods became super evident when we decided to take out our box-stock YZ250F (totally rebuilt and back from Yamaha’s Engineering Department) and compare the two. What we found was that our freshly rebuilt stock YZ250F was incredibly slow compared to the monster that Pro Circuit had built. We were shocked, because at the riders’ sensory level the power gains weren’t all that evident. Pro Circuit’s YZ250F  didn’t pull a higher gear through the corners, but it did demand that you upshift with more alacrity. It would pull so strongly and quickly through each gear that you wanted to catch the next gear just to see how fast you could go. Pro Circuit’s overall powerband was pleasant. Nothing arm-jerking, but plenty of power on tap to get you out of the trouble you found yourself in. If you didn’t feel comfortable catching the next shift right before a corner, the bike also had enough overrev on top to get there in a lower gear. On the dyno, Pro Circuit’s total engine rebuild produced seven more horsepower at peak, more power at every part of the curve (from idle to rev limiter) and beaucoup more over-rev on top. The funny thing is that when we were riding the Pro Circuit engine for the suspension tests, we couldn’t tell that it was fast. It had the same characteristics as our stock engine. It zinged through each gear, revved fast and turned over quick. But, in back-to-back tests, it ripped. Seven ponies is no small feat for an engine that only makes 35 horsepower in stock trim.

 THERE ARE VERY FEW HOP-UP PARTS FOR THE YZ250F, APART FROM EXHAUST SYSTEMS.

There is one important issue to address on the 2006 YZ250Fthe intake valves. Since its release almost six years ago, the YZ250F has been the most reliable bike imaginable. It has been bulletproof. The rash of intake valve problems in 2006 is not endemic to all years and models of the YZ250F. The only bike affected is the 2006 modeland Yamaha’s recall will take care of the problem. Pro Circuit is one of the world’s best hop-up shops (as their incredible string of AMA Championships proves), and they were never content to run the stock valve train. Pro Circuit was in the process of designing new valves, cams and pistons for the YZ250F before the intake valve problems became critical. MXA’s YZ250F was the first engine to get fitted with the Pro Circuit running gear.
Pro Circuit and the MXA wrecking crew came into the YZ250F project on the same wavelength. There are very few hop-up parts for the YZ250F, apart from exhaust systems. Why? That’s easy. From its inception in 2001, the YZ250F has been so good that few riders or hop-up shops ever felt the need to twang on it. But, for MXA and Pro Circuit, the time had come. The new breed of chunky powerbands, illustrated most ably by the KX250F and KTM 250SXF, had taken the patina off the mid-sized Why-Zed. Finally, after all these years, it needed to be twanged. And that is what this MXA wrecking crew project was all about.

We can tell you this. If Pro Circuit was a Yamaha-supported team, instead of Kawasaki, the first turn at every AMA 250F National would be a sea of blue.