Hot Cams Suzuki RM-Z250 Project Build

Jun. 03, 2014 By Scott Rousseau

Although shadowed in stock form by some of its more recently updated competition, the 2014 Suzuki RM-Z250 is still a great choice if you’re looking for a strong 250cc machine for motocross or off-road play. With its slim and light feeling chassis, the RM-Z250 is stable yet quick-steering, and its stock suspension can tame nasty terrain with aplomb.

A lack of low-end power is the main handicap an RM-250 rider will face when doing battle with the competition from Honda, Kawasaki and Yamaha. The RM-Z250 boasts a pretty stout 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 midrange thrust is a deficiency we don’t want to live with, especially on tracks that feature a big jump placed right out of a berm or flat turn.

Well, we didn’t want to live with it, so we phoned our long-time friend Jay Clark of Jay Clark Enterprises for some recommendations.

If you’ve never heard of Jay Clark, rest assured that he is a well-known aftermarket parts guru in the industry, having worked with a long list of aftermarket hardware companies and also working with Dunlop. If you’ve ever walked the pits at a Lucas Oil Pro Motocross Championship AMA National Motocross, you’ve probably seen him changing tires at the Dunlop tire truck. But that’s just one of the hats he wears, and when we asked for his help, he was happy not only to help us with our RM-Z250 woes, but he also offered to showcase two other machines. In addition to our RM-Z250, 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—in future installments.

Before we go any farther, however, it is important to understand that you are looking at a full-blown catalog racer here. Clark’s mission is to show off 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. That said, 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.

An FMF Racing Ti Megabomb header and 4.1 RCT Ti muffler with carbon-fiber cap help improve performance on our four-stroke-powered Suzuki.

Since the main goal was to beef up low-end and midrange performance without altering the overall power character of the bike, Clark took a fairly conservative approach to internal modifications. The cylinder head still features the stock porting and the stock valve sizes and valve springs, and it can run on the poor quality 91 unleaded gasoline found these days at local filling stations.

Instead, 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.  

Then, to build the power exactly how we wanted it, Clark called on a long-time partner, Hot Cams, which supplied a set of its Stage 1 cam sets. The Hot Cams 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 add strength and durability. Vertex also offers a high-compression Replica piston to pump up the RMZ-250’s power output, but fitting one eliminates the possibility of running pump gasoline.

Maybe 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 one we would never have thought of ourselves. Clark called on Injectioneering of Torrance, California, to recalibrate the RM-Z250’s 44mm throttle body. 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.

Injectioneering helped recalibrate the 44mm throttle body on the RM-Z250 to acutely fine-tune the bike’s power delivery.

The improvements to the RM-Z250’s throttle body are precise and labor-intensive, including a careful calibration of the throttle position sensor to within 1000th of a volt and a modification to the throttle spring tension to make the throttle more responsive through simple leverage. The RM-Z250’s throttle body is a taper bored throttle body, so Wilcox uses his own method of perfecting tolerances throughout the throttle body as well.  Wilson only charges $295 for what amounts to a lot of detailed work.

Adding to the RM-Z250’s sophistication and adjustability, 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.

Still, 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.

Moto Tassinari’s AIR4ORCE tunable intake boots help fine tune power delivery.

In the interest of better airflow management, one of Moto Tassinari’s AIR4ORCE tunable intake boots was also fitted to the RM-Z250. 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 hard-coated 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. 

Although the RM-Z250 doesn’t have any massive needs in the handling and suspension department, Race Tech was employed to re-valve the RM-Z to fine tune the suspension.

Our biggest concerns with the stock RM-Z250 motor. Like we said at the start, we couldn’t be happier with its chassis and suspension, but since Clark works with a laundry list of companies whenever he builds a bike, it was inevitable that the RM-Z250’s suspension would get a massage by one of the aftermarket suspension firms that dot the Southern California landscape. In this case, Clark chose Race Tech to re-valve the RM-Z to his preferences. We’re not going to get into the particulars of Race Tech’s work here, because every rider has different needs. Our suggestion is that you contact Race Tech directly to discuss your own personal concerns with your suspension and work with them to come up with the right solutions.

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.

Clark also added some premium aftermarket wheels to the RM-Z250, 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. 

The Raptor titanium footpegs on the RM-Z250 may be a bit over the top, but then again these lightweight pegs are just as strong as steel and provide some additional traction when it’s needed most.

While all of the parts on this project RM-Z250 are high-quality, few reach the ridiculously 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 as light as a feather, but they’re also strong as steel and 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. However, at $354 per set, they’re pricey.

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.

Our test rider Ryan Abbatoye put the project RM-Z250 through its paces at Comp Edge Raceway.

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 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 
MX 32 front 80/100-21, $120.89
MX 32 rear 110/90-19, $134.04-149.25

Vertex Pistons 
Replica Forged Standard Comp Piston kit, $191.05   

Hot Cams       
Stage 1 Intake Cam, $179.95
Stage 1 Exhaust Cam, $199.95     

FMF Racing   
Factory 4.1 RCT Ti Muffler w/carbon cap, $549.99  
Ti Megabomb header, $349.99    

Throttle Body Modifications, $295     

Air4orce air boot, $298      

Renegade Racing Fuels
SX4, call for pricing

Vortex Ignitions      
X-10 ECU, $699.95

Uni Filter   
RM-Z250 Air Filter, $30.95     

Formed Silicone Coolant hose kit, $139.62
High pressure radiator cap, $22.73

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                                             
Semi-Custom Graphics kit w/pre-printed numberplates, $269.90                      

Moto Seat   
Two-Tone seat cover, $49.95

Works Connection  
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         
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 
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  
Suspension re-valve and set up, call for consultation

Raptor Titanium
Ti footpegs, $354.95 Newsletter
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