Honda's Crf250r Goes Digital
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 predictable 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 coldstarting 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. -Kevin Cameron
