By comparison, the modifications and updates done to the 2009 Yamaha YZ250F may seem mild. Other brands are releasing much more made-over versions of their Lites-class weapons, and 450s are quite revolutionary this year. So why would you go to the blue crew in '09 if you're riding a 250F? Because it seems everything they've changed is working.Do Yamahas have a turning issue? Up to this point, the accusation that they do could be successfully argued. Although we've been able to get both sizes of the YZ-F motocrossers to turn well (with some of the fastest lap times in our shootouts), we're not about to claim they're the easiest to get along with in the corners. Bike setup has been critical in the past, especially for the lighter 250F which seems to be in for more of a fight in the handling department than its bigger brother the mighty 450. This really becomes obvious when you get ahold of 2009 models.While both of Yamaha's full-size MX bikes received almost identical updates in the chassis, the YZ250F gets more of a motor-based makeover with a new clutch assembly and exhaust system. Yamaha engineers must have grown sick of hearing about the soft bottom-end power on last year's bike because all of their updates are aimed at boosting the bottom while preserving the YZ-F's mid-to-top prowess.The simplest, and cheapest, way to make more power is to modify an exhaust system. They're easy to test (since you don't have to tear apart a motor for different settings), and they're almost endless in their tunability. Yamaha settled on an exhaust system design that tuned up the YZ250F in two steps, or maybe three depending on what you count.First, the header is 60mm longer right as it exits the motor, before the first bend. Next, the muffler is 50mm shorter. This loss in muffler length is in a crucial place; it's the last section of the muffler that's shorter. Or the part that hangs out the most. From the muffler mount forward to the midpipe, the muffler is almost identical to the '08 unit. Last, the steps in the header are gone and now the exhaust system stays a consistent diameter throughout the midpipe.These are small changes, sure, but they make a big difference on the track. Our first testing feedback told us the Yamaha was awake down low where it once was asleep. It's not the gnarliest motor out of the corners or when accelerating hard by a long shot. But what it still may lack in snappy excitement it will more than make up for in traction and forward drive. This is a step in the right direction and much more than a baby step. When ridden back to back with our '08, the improvements were substantial.Carburetion tweaks seem to have the motor running crisper on the track as well. In fact, the entire motor is quieter and much smoother running than our '08 was a year ago. No doubt the enhanced ignition mapping in the new bike is assisting with this improvement. More than one (in fact, most) test riders commented negatively about the engine noise and rough-at-times running on last year's model. So far, the issue hasn't come up with the new Yamaha.The new internal clutch system may have more to do with this better-sounding engine than anything. Previously, the Yamaha 250F clutch had a judder-spring-damped engagement. Also, the six coil springs on the back of the basket have been replaced with eight rubber bushings for 2009. Steel clutch plates throughout the clutch pack are now identical, whereas last year's spring-damped system required a thicker steel plate against the inside of the basket. Overall, the new clutch assembly should have a longer service interval (due to there being no steel-on-spring contact creating contamination in the oil bath) and surely there will be less heat and noise. With all those benefits of the new clutch, the one you'll enjoy most might be the simple engagement of it all.The new clutch bites solidly and quickly with a narrower modulation window at the lever. Engine power is delivered directly to the ground immediately. For some, this engagement might be too fast. But for all DR testers so far, this is proving to be a great power enhancer. At around eight hours of run time the clutch is showing zero signs of fade (and that's with a seasoned professional, a lazy magazine editor and a hyperactive 15-year-old intermediate abusing the beans out of it). Our '08 clutch didn't hold up as well.But what about the handling? Does it turn or what? The fast answer to that is yes. It turns quite well, actually. And much better than the previous YZ250Fs. If you've been paying attention, you know all there is to know about Yamaha's new swingarm and linkage. If you haven't, here's a recap: It's now hydroformed and engineered for more flex up and down (as two prongs of a fork moving vertically in unison as well as alternating up and down like a swimmer's legs). Also, it has more side-to-side or horizontal rigidity. The linkage is redesigned to complement and mate up with the new swingarm yet its ratio is identical to the previous year's model.