2007 Honda CRF450X Project Bike Part II

October 3, 2007
JC Hilderbrand
JC Hilderbrand
Off-Road Editor|Articles|Articles RSS|Blog |Blog Posts |Blog RSS

Hilde is holding down the fort at MotoUSA's Southern Oregon HQ. With world-class dirt bike and ATV trails just minutes away, the hardest part is getting him to focus on the keyboard. Two wheels or four, it doesn't matter to our Off-Road Editor so long as it goes like hell in the dirt.

2007 Honda CRF450X Project Bike
Our 2007 Honda CRF450X Project Bike continues to evolve. This installment covers some simple, but very important modifications to the motor and exhaust.

Like any good non-Californian, the first thing we wanted to do with our 50-state legal 2007 Honda CRF450X was yank all that emissions crap right off. Of course, it isn’t quite as simple as removing the existing hardware seeing how a hole in the side of the cylinder is typically not conducive to a smooth-running machine. While our suspension was being worked over by Watson Performance, we called up some of the most successful 450X racers we could think of to explore our options.

Precision Concepts has made the switch from kicking ass primarily on XR650R machines to the more modern, lighter and versatile CRF-X. Bob Bell and his crew race just about every kind of off-road competition you can think of – desert, motocross, WORCS, you name it – and they do it on the 450X. These guys helped us out with our Baja Project a couple years ago, and as we’ve continued to deal with the Murrieta, CA-based company, we are convinced that finding anyone with more testing hours on our particular machine would be quite the challenge.

Though pulling off the emission controls requires the purchase and installation of some aftermarket components, the process itself is simple enough for even the most rudimentary mechanics. We had PC’s master engine guru, Eric Siraton, walk us through the steps for a successful transformation to closed-course specs using the Precision Concepts Block Off Kit.

In stock form, the CRF-X is pretty asthmatic to say the least. We had problems with the lean jetting and it was obvious that what could be a fun enduro mill was unhappily choked up. Popping on deceleration was annoying more than anything, but a serious hesitation when mashing the throttle, especially off idle, created our biggest performance issue.

ISDE silver-medalist and MotoUSA test rider, Mason Harrison, appreciated the Honda’s slim ergonomics, strong brakes and desire to be aggressive. However, wanting to be aggressive and managing to do so with the response problems are completely different.

“I really like the Honda,” says Harrison, “but it’s really just a decent trail bike in stock condition. You would need to really uncork it in order to make it more of a race bike.”

Cutting out the top of the airbox and the left side-panel vent drastically improve the amount of airflow. We had to find a way to get more fuel into the motor as well.
Cutting out the top of the airbox and the left side-panel vent drastically improve the amount of airflow. We had to find a way to get more fuel into the motor as well.

Even with the block-off kit, many riders opt to go further and cut the airbox for better flow. We wanted to use this project bike as a race steed for a couple WORCS rounds, local hare scrambles and possibly a stint in the AMA EnduroCross series, so we figured it would be worth the extra effort to go full-tilt. Since we were logging hours in the garage anyway, we unbolted the subframe, disconnected the mess of electrical harnesses and busted out the Dremel.

Transforming the X-model airbox into a closer version of the CRF-R machine is as simple as cutting on the dotted line. We opted for the full airbox cut rather than simply trimming out the side panel. A seam along the inside of the airbox makes for a simple guide to follow, and there is only one area where you have to think for yourself and use some common sense. Siraton certainly has a steadier hand than us after cutting as many X-models as he has, and our cut surely wasn’t as factory-looking as his. The Red Rider expert recommends using a die grinder with full-sized cutting wheel followed by the Dremel to clean things up.

“The lower the speed the more it digs in, the higher the speed the more it skims the surface,” he cautions. “Be very light with the hand – no pressure.”

After doing our best Texas chainsaw impression, we definitely weren’t bragging about our smooth lines to PC. A little sandpaper helps tidy up, but make sure to clean the airbox with extra care after the cut to make sure all plastic shavings are removed. Reinstall the airbox and subframe and it’s time to adjust the carb for all that extra atmosphere. Siraton gave us a couple options to choose from for re-jetting our non-Cali Honda.

Dubach Racing s stainless steel aluminum SA System exhaust was just what the doctor ordered to spice up the look  sound and performance of our 450X.
Dubach Racing’s stainless steel/aluminum SA System exhaust was just what the doctor ordered to spice up the look, sound and performance of our 450X.

Since we had done the complete airbox mod, block-off kit and had a Dubach Racing full-system exhaust in the mail, we utilized Precision Concepts’ low-desert arrangement (sea level to 1500 feet elevation). The combo includes a richer NCYS needle in the fourth clip position to replace the fixed-position stocker, a larger 165 main jet and standard pilot (45). They also recommend a 65 leak jet, but we originally tested without it. The reason for a smaller leak jet is to monitor the low-rpm fuel intake which is a bit heavy with the richer needle. All the extra fuel getting dumped in creates a bog at low rpm. We didn’t have much of an issue with that because the problem area was low enough in the rev range that we never actually experienced it while riding. However, we did find that the airbox mods and DRD exhaust system were actually flowing too much air, and even with the richer jetting we experienced some lean popping. We had our Ignition Products dB Dawg in the toolbox and the insert worked perfectly to restrict just enough exhaust flow to clean up the motor performance. More on the full-system stainless steel/aluminum DRD SA System exhaust in a forthcoming product review.

Once the jetting issues were finagled into working order, the CRF450X was really livened up. The simple formula of dumping more air and fuel into a motor makes sense that it would perk up the performance. That’s exactly what happened with our CRF450X when the Precision Concepts Block-Off Kit and jetting and airbox mods were combined with a new exhaust system. Not only did the DRD exhaust give it a better bark, but the actual bite was improved as well along with a 3.5-pound weight saving over the stock unit. The X still doesn’t hit as hard as one of Honda’s R models, but the increased snap makes getting over off-road obstacles much easier, and clearing jumps on the WORCS courses required less effort as well.

Riding the 450X in a pair of Pacific Northwest WORCS races has given us affirmation that we re moving in the right direction with the project.
Riding the 450X in a pair of Pacific Northwest WORCS races has given us affirmation that we’re moving in the right direction with the project.

“It definitely isn’t as rowdy as a full-on moto bike,” says MotoUSA’s Creative Director, Brian Chamberlain. “I’d actually like it to have a little more pop just for the extra grin factor, but as far as being a good woods bike, this actually gets the job done pretty well – much better than the stocker. All of the mods were simple to do and I especially like the look and sound of the DRD pipe. You can actually hear yourself on the starting line!”

One of the most endearing features of any enduro bike is the fact that they don’t rip your arms out, so all-day riding and technical sections are more manageable. Our stock motor was a good trail bike, but our new configuration took a few steps towards making this bike a capable enduro racing machine. Combined with our suspension mods from Part 1 of this CRF450X Project Bike, we’re starting to get pretty attached to our long-term Honda.

2007 Honda CRF450X Parts List:
Precision Concepts Block-Off Kit – $39.99
Precision Concepts Ventilation Kit – $29.99
NCYS Needle Jet – $19.78
65 Leak Jet – $6.47
Dubach Racing full SA System Exhaust – $549.95

Let us know what you think about the 2007 Honda CRF450X Project  in the MotoUSA Forum.