Aftermarket bike builder Jay Clark puts together one fat Suzuki RM-Z250.
Compared to some of its more recently developed competition, the 2014 Suzuki RM-Z250 is no longer the sharpest tool in the shed for quarter-liter motocross work. Blessed with a slim and light feeling chassis, the ‘Zook can still turn circles under some of its rivals, and its stock suspension is able to tame whatever nasty terrain that happens to rush under its wheels.
So, what’s our beef? Well, our beef is the beef. Power. And not even really a lack of power but rather power placement. The RM-Z250 boasts a pretty shiny top-end, but its low-end punch is a little weak and its transition through the midrange is lackluster compared to other bikes in its class. Keep its DOHC, four-valve engine screaming, and you can cut lap times with the best of the stock 250s in the pack, but you’ll work harder to do it. Corner to corner, the lack of low-end and mid-range thrust is a handicap we don’t want to live with, especially on tracks that feature a big jump placed right out of a berm or flat turn.
And guess what? Thanks to the flourishing aftermarket. We don’t have to. There are plenty of companies who love the RM-Z250 as much as we do and are willing to pitch in and help pump up the RM-Z250’s motor to help that sweet chassis reach its full potential. In our case, that meant placing a call to our long-time friend Jay Clark of Jay Clark Enterprises for some recommendations.
Clark is a well-known fixture in the industry, having worked with a long list of aftermarket hardware companies and also with Dunlop. In fact, our idea to work with him was actually hatched earlier this year when we attended the Dunlop MX32/MX52 tire launch. When all was said and done, we had a program in place to showcase three bikes using Clark’s connections. In addition to our RM-250, you’re going to see the magic that Clark worked with the 2014 Kawasaki KX450F and also an older but still relevant 2006 Honda CRF450X—our personal favorite of the three.
But first, a caveat, because as consumers ourselves, we know how project machines such as this one are so often viewed. Some folks will take one look at full-blown catalog-style bikes such as this RM-Z250 and scoff, reasoning that nobody but nobody could afford all of the parts on our list, and since attempting to build such a machine would break the bank, we shouldn’t be showing it to you in the first place. We can concede that to a point—after all, it is sort of like saying that Chrysler shouldn’t keep building bitchin’ trucks because now that I’ve seen the new Power Wagon, I really want one, but I can’t afford one and it really makes my old Ram 1500 look bad by comparison. Bottom line, Clark never does anything half-assed, and his job is to showcase as many parts as he can for the companies he represents. With that in mind, this particular RM-Z250 would require a substantial financial commitment to replicate.
On the other hand, a little careful shopping can yield a lot of these parts at prices substantially lower than the MSRP. Clark, for example, works with Rocky Mountain ATV/MC, one of the top discount aftermarket parts and apparel suppliers in the industry. We’ve published manufacturer suggested retail prices for all of the parts here, but shop around and you’ll be surprised at how much you can save. For example, we can tell you that the wheel supplier for our RM-Z250, Tusk Off-Road, sells its complete wheel kits and brake parts at prices far below the published list price—log onto the Rocky Mountain ATV/MC website here to see just how low. Finally, look past the bling and you’ll see there are some really smart modifications that wake up our RM-Z250 and make it perform like we wish the stock machine did.
Engine
We’ve already outlined our issues with the engine performance of our stock RM-Z250, and regardless of how it looks, Clark’s main goal was to beef up low-end and midrange performance without altering the RM-Z250s top-end rush. There is no cylinder porting involved here, and the engine still uses the stock valve sizes and valve springs and can run on the swill that passes for 91 unleaded gasoline these days at your local pumps.
Clark started by following the first commandment of power tuning a four-stroke, that if you want to get more air through the engine, make sure it has a way to get out of the engine. So, starting at the rear, he chose FMF Racing’s top-shelf Ti Megabomb header and Factory 4.1 RCT Ti muffler with carbon fiber cap. FMF has a long and storied history of producing systems that improve horsepower and torque. Make no mistake, these two items aren’t cheap, but they pinnacle of FMF’s expertise in exhaust system design. FMF offers basically the same systems constructed of less-exotic materials for performance-minded riders on a budget.
To get the power to build right where we wanted it, Clark called on a long-time partner, Hot Cams, which supplied a set of its Stage 1 cam sets. Stage 1 cam sets are designed to increase low-rpm torque, where the RM-Z250 needs it most. Since the motor was torn down anyway, Clark also added a Vertex Replica piston kit. The Vertex piston retains the same compression ratio as the stock Suzuki piston, but it is a forged unit, and forged pistons represent the height of strength and durability. If you are looking for even more power, Vertex offers a high-compression Replica piston for the RMZ-250, but fitting one will mean running a strict diet of race gas.
In our opinion, one of the smartest mods made to this particular RM-Z250—and perhaps the first place we would start if we were on a strict budget—was a recalibrated 44mm throttle body, which was handled by Injectioneering of Torrance, California. Injectioneering proprietor Wade Wilcox has been working with fuel injection since the advent of Honda’s turbocharged CX500 in the early 1980s, and he knows just what needs to be done to optimize the RM-Z’s throttle body.
“The Suzuki already has a pretty good solid body, but the biggest room in the world is room for improvement,” Wilcox says, and then jokingly adds, “I stole the last part of that line.”
But his improvements to the RM-Z250’s throttle body are serious and labor-intensive.
“People say that the RM-Z250 is not snappy enough coming out of the corners,” Wilcox says. “I enhance that ability and improve throttle response by carefully calibrating the throttle position sensor to within 1000th of a volt and reducing the throttle spring tension to make the throttle more responsive through simple leverage. Also, the RM-Z250’s throttle body is a taper bored throttle body, so I use my own method of perfecting tolerances throughout the throttle body.”
For all that work, Wilson only charges $279. It is important to note, however, that if you want an Injectioneering-doctored throttle body, you have to supply the stocker yourself. Wilcox does not work on an exchange basis.
Moving from the sensible to the stupendous, Clark fitted the RM-Z250 with a Vortex ignitions X-10 ECU, which not only controls spark timing and voltage output but also provides a way to precisely tune the fueling for improved power and easier starting. The X-10 comes pre-programmed with 10 performance fuel and spark timing maps and can adjust the fueling via three switches that cover the low, mid and full throttle openings. The unit is also fully programmable to a mind-boggling degree via accessory Vortex software, allowing the user control over rev limit, throttle enrichment and decay time, fuel timing, mapping, ignition dwell timing, voltage output and trim tables for cold starting, air intake, barometric pressure, voltage output and more. In addition, many of these parameters are data-logged in real time, and can be viewed via a PC through a USB port.
But, for all of its sophistication, the Vortex X-10 is still a simple bolt-on item. It plugs directly into the RM-Z250’s standard wiring harness and comes with all the necessary mounting hardware supplied. The Vortex doesn’t come cheap. The high-tech X-10 will run you about $699.95, but if you need ignition and fuel control capabilities that rival those of the factory teams, it’s worth a look.
Clark also fitted the RM-Z250 with one of Moto Tassinari’s AIR4ORCE tunable intake boots. The AIR4ORCE replaces the stock airboot and included adjustable velocity stacks that offer one more way to fine tune the power delivery based upon rider preference and/or track conditions. According to Moto Tassinari, AIR4ORCE systems are currently used by the Monster Energy Kawasaki, GEICO Honda and Troy Lee Designs/Lucas Oil/Honda teams. Inside the AIR4ORCE is a Uni-Filter RM-Z250 replacement air filter.
To spruce up the engine compartment a little more, Clark added a CV4 formed silicone coolant hose kit and topped the radiator with one of CV4’s high-pressure radiator caps. He also added some trick-looking bits from Works Connection, including their radiator braces, engine plugs, oil fill plug, engine hour meter and hour meter mount.
Knowing that the RM-Z250 now had the potential to put more power to the ground, Clark wanted to make sure that it got there consistently, so he also installed a complete Hinson Racing Billetproof clutch kit. Hinson Racing clutches have been used by most major factory teams in motocross and off-road. Hinson says that its components are precision machined from billet T-6 aircraft quality aluminum to aerospace tolerances, and hardcoated for five times the wear resistance to stock when properly maintained. The precise tolerances allow the clutch assembly to spin truer, creating less heat when clutch is disengaged and providing a more positive, smooth clutch engagement.
The complete kit includes a billet clutch basket, clutch hub and pressure plate, along with a full Hinson FSC clutch and spring kit and a Hinson Racing clutch cover. At $1089.99, it is slightly less expensive to buy the full kit at once, we’ve published the individual components in case you might want to piece it together.
Suspension/Accessories
Beyond the suspension work, this RM-Z250 features accessories with a whole lot of bling to match their performance. The RM-Z’s Showa front fork his held in place with an Applied Racing aluminum triple clamp capped by Renthal’s 997 Twin Wall handlebar, which rides in Renthal Big Bar mounts. The bar also wears Renthal Dual Series grips and Works Connection’s Elite lever perches. Drive duties are handled by Renthal as well, with a stock replacement Renthal front sprocket transmitting power to a 48-tooth rear sprocket via an R1 Works chain.
This RM-Z also features some premium rolling stock in the form of Tusk Off-Road’s Impact wheel kit, which features anodized hubs for a sexy look. The rear wheel is located by Works Connection axle blocks. Tusk Off-Road also supplied more braking power via its Typhoon 270mm oversized floating rotor kit and Typhoon stainless steel rear brake rotor, and Clark beautified the front and rear brake reservoirs by adding Works Connection reservoir caps to each. Naturally, the front and rear tires are Dunlop’s latest MX32s.
All of the parts on this project RM-Z250 are high-quality, but few reach the exotic levels of the Raptor titanium footpegs that Clark spec’d on the bike. Tipping the scales at a mere 410 grams per set, they’re a weight weenie’s dream, but beyond their featherweight material, they’re also well-designed. The 57mm wide platforms feature a central brace of 3mm teeth on each peg to offer more traction for the rider’s boots. But at $354 per set, we’re talking about a big commitment.
Finally, the overall aesthetics of the bike are enhanced by a DeCal Works Semi-Custom Graphics kit and a Moto Seat Two-Tone seat cover made of material that offers more traction than the stock seat cover.
Riding Impression
Clark invited us out to Comp Edge Raceway near Hesperia, California, so that we could swing a leg over the modified RM-Z250. During our short ride, we focused mainly on the engine performance, and DirtBikes.com test rider Ryan Abbatoye came away impressed with the improvements.
The modded motor sounded much healthier through the FMF exhaust when we fired it up, but after a few sorting laps, Abbatoye came in and told Clark that it felt as if the engine was still feeling a little thin on the bottom, as if it was running a little lean. Clark quickly tweaked the Vortex X-10 ECU by richening up the low-range fueling and sent Abbatoye back out for a long and happy moto.
With its healthier bottom end and improved mid-range pull, Abbatoye was able to launch out of short chutes and up and over big jumps much more easily than with the stock RM-Z250 we had along for comparison, noting that the modified motor’s overall performance was more pleasing from bottom to top without losing its smooth character. The added power meant less shifting, which equates to a better riding experience, similar to the stock 2014 Yamaha YZ250. He also noticed that Hinson clutch felt much better through the lever than the stocker, and we are already familiar with the Hinson’s ability to handle abuse.
Overall, our riding impression concluded that the Suzuki RM-Z250 can still be a contender with the right modifications. You certainly don’t have to throw all of the parts you see here to get it that way, but certainly the throttle body, ignition, cams and pipe are all excellent places to start. We have no doubt that Suzuki riders can still find their way to the front of the pack without them, but money spent in the right areas will yield a much stronger motorcycle.
2014 Hot Cams/FMF/Dunlop MX32 Suzuki Project Parts List
Dunlop Tire www.dunlopmotorcycle.com, 800-845-8378
MX 32 front 80/100-21, $120.89
MX 32 rear 110/90-19, $134.04-149.25
Vertex Pistons www.vertexpistons.com, 515-270-2302
Replica Forged Standard Comp Piston kit, $191.05
Hot Cams www.rockymountainatvmc.com, 800-336-5437
Stage 1 Intake Cam, $179.95
Stage 1 Exhaust Cam, $199.95
FMF Racing www.rockymountainatvmc.com, 800-336-5437 800-336-5437
Factory 4.1 RCT Ti Muffler w/carbon cap, $549.99
Ti Megabomb header, $349.99
Injectioneering www.injectioneering.com, 310-953-2915
Throttle Body Modifications, $295
MotoTassinari www.rockymountainatvmc.com, 800-336-5437
Air4orce air boot, $298
Vortex Ignitions www.vortexcdi.com
X-10 ECU, $699.95
Uni Filter www.rockymountainatvmc.com, 800-336-5437
RM-Z250 Air Filter, $30.95
CV4 www.cv4.net, 800-874-1223
Formed Silicone Coolant hose kit, $139.62
High pressure radiator cap, $22.73
Renthal www.renthal.com, 877-736-8425
Stock front sprocket, $25.95
Rear 48T sprocket, $69.95
R1 Works Chain, $85.95
997 Twin Wall Handlebar, $199.95
Dual Series grips, $15.95
Big bar Mounts, $59.95
DeCal Works www.decalmx.com, 815-784-4000
Semi-Custom Graphics kit w/pre-printed numberplates, $269.90
Moto Seat www.motoseat.com, 951-258-5229
Two-Tone seat cover, $49.95
Works Connection www.worksconnection.com, 800-895-8292
Elite Perch, $79.95 each
Front brake cap, $27.50
Rear Brake cap, $24.95
Radiator Braces, $89.95
Axle blocks, $49.95
Engine plugs, $39.95
Oil fill plug, $24.95
Hour meter, $39.95
Hour meter mount, $14.95
Factory II Stand, $119.95
Hinson Clutch Components www.hinsonracing.com, 909-946-2942
Billetproof Clutch Basket, $274.99
Billetproof Inner Hub, $309.99
Billetproof Pressure Plate, $189.99
FSC clutch plate & spring kit, $199.99
Billetproof clutch cover, $169.99
Tusk Off-Road www.rockymountainatvmc.com, 800-336-5437
Typhoon 270mm oversized floating rotor kit, $149.99
Typhoon stainless steel rear brake rotor, $99.99
Impact complete front/rear wheel kit, $729.99
Race Tech www.racetech.com, 951-279-6655
Suspension re-valve and set up, call for consultation
Raptor Titanium www.raptortitanium.com
Ti footpegs, $354.95
Your Privacy Choices