2010 Honda CRF250R: Fuel Injection without Weight Infection

    Cycle World
    Feb 01, 2010

By: Kevin Cameron

You wanna talk new? Okay, how’s this? Except for the wheels, tires and an assortment of nuts and bolts, everything on the 2010 Honda CRF250R is all-new. Everything. The engine is a complete redesign, as are the frame and suspension, and even the bodywork is new. Not only that, this Lites-class Honda now is the first 250cc motocrosser to be fuel-injected rather than carbureted. And it’s not just another typical fuel injection; this is the most impressive system ever used on any MX bike.

It’s impressive for a couple of reasons. The EFI noticeably improves engine performance, which is a hugely important factor in a motocross class where power means so much more than it does on bigger bikes. The injection also functions flawlessly, never guilty of a single blubber, bog or hiccup as it shoots a sharp, crisp exhaust note out of the single muffler that replaces the previous model’s twin pipes. Further, the system’s precise fuel metering gives the rider a greater sense of throttle-to-rear-wheel control. Perhaps best of all, Honda was able to make the switch from carburetor to fuel injection without increasing the bike’s weight. Our test 250 tipped the scales at 217 pounds, exactly the same weight as the 2009 model, and it actually feels even lighter than the ’09 when you ride it.

Credit a more-focused program of mass centralization and a lower center of gravity. Honda did not accomplish this feat with radical designs, such as the “backward” engine on Yamaha’s new YZ450F—although the CRF250R already utilizes the offset crankshaft design proudly boasted by Yamaha. Instead, Big Red’s engineers made the 249cc Unicam engine even more compact than before. The engine is vertically shorter, achieved by means of a thinner piston crown, along with a relocated crankcase breather that allowed the crankshaft to be lowered in the cases by 10mm. The intake ports are now straighter, the bore and stroke were changed from 78.0 x 52.2mm in ’09 to 76.8 x 53.8mm, and the compression ratio has gone up from 13.0:1 to 13.2:1.

On the track, the 250R’s outright power seems about the same as that of last year’s bike. Jumps that require full-throttle acceleration off corners launch the new 250 as far as the previous one, and wide-open runs from corner to corner also are roughly equal. But the new bike’s power can be deceiving; the fuel-injection system smoothes delivery so much that the abrupt, snappy power of the previous bike is history.

This has an effect on the way you ride the new 250. On the carbureted model, you turned the throttle, usually wide-open, then waited for a fraction of a second for a big hit to show up; but on the injected bike, you get immediate results when you twist the grip, and the amount of power that arrives is pretty much proportional to how far you open the throttle. So, there’s no need to be wide-open constantly like on the previous 250F; instead, you ride the new bike a lot like a 450, because it is more sensitive to throttle position and always ready to make power. Actually, even the 450s haven’t felt as good, engine-wise, since they generally have too much power for you to fully appreciate—or even sense—truly spot-on fueling.

In fact, all aspects of the CRF’s performance are more sensitive to rider input. The new twin-spar aluminum frame is a mere 1mm narrower and 4mm lower, but revised steering geometry moves the front wheel 0.6-inch closer to the crank-shaft, while the wheelbase is claimed to be 0.6 inches longer. Triple-clamp offset was shortened from 22mm to 20mm, with rake and trail going from 27.9 degrees/4.9 inches to 27.3/4.6.

All this makes for a sharper-handling bike that corners with more precision and accuracy. The only possible draw-back is the loss of some high-speed stability. The new bike is busier coming into bumpy corners off of a fast section, whereas the old bike tended to stay straighter and have less of a reaction to braking bumps. But I was able to dial out most or all of those headshakes by turning up the Honda Progressive Steering Damper (HPSD) a couple of clicks.

Overall, it takes less effort to make the bike go where you want it to go than it did on the ’09 model. As mentioned earlier, the new bike acts as though it’s even lighter than it is, and excellent front-to-rear balance gives it a very neutral feel. This makes it easier to change direction in midair, and the bike flicks side to side with less effort, allowing quicker directional changes when on the ground. But because the CRF is more sensitive and makes instantaneous reactions, it’s not as forgiving, so the rider has to be on his/her game more than before.

Fortunately, improvements to the suspension help reduce the negative outcome of a rider’s poorly thought-out moves. Honda has stayed with Showa components at both ends but upped fork diameter from 47 to 48mm while retaining the ’09 bike’s 12.4 inches of travel. The shock, meanwhile, gets a larger piston and now delivers 12.6 inches of wheel travel (up from 12.4) as it works on a lighter swingarm and a redesigned Pro-Link linkage.

This suspension package provides solid tracking out of corners with no kicking or packing. Both ends are more plush, so there is no real harshness when hitting sharp bumps or landing off skyscraper jumps. To suit my riding style, I opened up the shock’s high-speed rebound one click and stiffened the fork’s compression by two clicks. At those settings, the suspension worked great for me, but it has enough adjustment range that it can accommodate riders of most styles, sizes and skill levels.

And so can the engine. Despite being “only” a 250, the CRF’s easy-to-start engine is actually more user-friendly than ever for less-experienced riders, thanks mostly to the fuel-injection system, yet it makes enough power to keep experts running up front. That’s the kind of flexibility that helps separate winners from also-rans.

Whether or not the CRF250R proves to be the class of the class remains to be seen in a future comparison. But with this bike, Honda has proven that a 250cc four-stroke can be successfully fuel-injected without any loss of power, but also without gaining weight, all while making the CRF250R a better motocross racer than it already was.

Honda’S CRF250R goes digital
Better riding through fuel injection

Getting carburetors to accurately deliver fuel in motocross has historically been quite difficult because of the challenging conditions. Bumps, jumps and zero gravity get float-bowl fuel sloshing around in such a way as to make it nearly impossible to guarantee predict-able engine response 100 percent of the time.

Fuel injection changes this completely.
Because the CRF250R’s PGM-FI system monitors throttle position, air and coolant temperatures, plus intake manifold pressure and rpm, its base performance is equivalent to attentive, accurate tuning by a carburetion expert. In addition, ignition timing is derived not from advancing or retarding the stator plate with little taps from your 2-ounce ball-peen hammer but from a stored internal electronic map. That means 1) a closer match of ignition timing to what the engine really needs; and 2) once you have the equipment for altering fuel and timing maps, you can change performance in specific areas of the engine’s powerband. This brings the tuning accuracy of MotoGP to motocross.

I spoke with American Honda’s Ray Conway about the new fuel system. “The real question is, what does this new technology let us do?” he began. “It’s not just the old bike plus fuel injection. This 250 has a bigger airbox, a smaller gas tank—this is an all-new motorcycle.”

Single-cylinder engines always need more airbox volume than there is room, and more accurate, more efficient fuel delivery allows the gas tank to shrink. The 76.8 x 53.8mm cylinder takes big gulps of air—big enough to pull air out of a too-small airbox faster than the box’s snorkel can make it up. Big is good.

I also wanted to know what MX-specific performance advantages injection brings. For instance, how about the zero-gravity situation in midjump?

“The 2008 and ’09 carbs on the 250 were good, but we fought a bog,” said Conway. “With a carburetor, a jump makes the fuel go one way and the bike the other—even with complicated float baffles and plastic jet hoods.

“Aside from not needing altitude and weather tuning and cold-starting so well, a real advantage is no springtime carb cleanout,” he added. “You just drain the old gas, fill up with fresh and go.”

The same 50mm throttle body serves both the 450 and 250, and the 250 injector nozzle is a 12-hole Keihin. Injection pressure is 50 psi. A larger AC generator provides the extra power needed by the system. Dual crank-position sensors identify the compression stroke and piston position.

Okay, the system compensates for weather changes, but what if you want to tune in modified cam timing or a different compression ratio?

“Tuning uses the PGM-FI Setting Tool,” Conway replied. “There’s base data for mixture and ignition timing, and the kit lets you make changes using a (Windows) laptop. This isn’t just for power; you can soften the power for a new rider or a slick track. On the Internet, you can download settings used by name riders, and our service guys have written useful advice and tips.”

A serial USB connector for the setting tool’s wire loom is located behind the bike’s radiator shroud. Dude! No iPod docking port? Put your jets and needles away. Cell phones weren’t that tough. Neither is digital fuel injection.


Copyright ©2010 Hachette Filipacchi Media U.S., Inc. All Rights Reserved.
For more information about reprints from CycleWorld, contact Wright's Media at 877.652.5295.

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