The KTM line of four-stroke dual sport motorcycles is right at the top of the list in any given displacement category, but for riders looking to squeeze a bit more performance than the stock machine offers, custom dirtbike builder Jay Clark has come up with a recipe for success.
As Clark, owner of Jay Clark Enterprises, admits, the KTM 350 EXC-F isn’t the easiest bike from which to pull huge gains, but only because the stock machine is so good already.
The KTM EXC line of bikes is simply amazing for dual sport usage, but we thought we would tinker with our 350 EXC-F to see just how good we could make it for the trails,” Clark said. “There really isn’t much that you have to do to a KTM 350 EXC-F because the bike already has plenty of power for the track or the trail.”
Unlike a lot of Clark’s projects, which feature a host of internal engine mods, this particular KTM doesn’t boast any internal changes such as a camshaft or piston swap. Instead, Clark focused on shaping the power from the outside. The first order of business was to remove the backfire screen in the KTM’s stock airbox, thus improving air flow into the engine. He also used a stock KTM two-stroke air filter cage, which further decreases air restriction in the stock airbox and allows the engine to produce a bit more low-end snap for a lively feel off the bottom. Air filtration is handled by a Uni Filter two-stage air filter. In the clutch department, Clark beefed things up by going with a Hinson Racing full inner hub and pressure plate kit, fiber plates, steel plates and springs along with an outer clutch cover kit.
Even so, this KTM does sport two significant upgrades, one in the ignition department and the other with the exhaust. For the ignition, Clark went with a Vortex X10 ECU from Twisted Development, which allows the user to tailor the ignition spark timing and voltage output but also fuel mapping for more power. The X10 features 10 pre-programmed fuel and spark timing maps, but it features three additional switches to allow the dialing-in of the fuel curve at low, mid and high throttle openings. The X10 is a simple plug-and-play ECU, connecting directly into the standard KTM wiring harness to interface with all the standard engine sensors such as ECT (Engine Coolant Temperature), IAT (Intake Air Temperature), MAP (Manifold Absolute Pressure), TPS (Throttle Position Sensor), CPS (Crank Position Sensor), so that it can automatically adjust fuel and spark timing for optimum power delivery in all weather, altitude and load conditions. When combined with the Vortex’s accessory software, the ECU can also be programmed to allow modification of several parameters, including rev limit, throttle enrichment and decay time, fuel timing, high resolution mapping, dwell time, voltage output and trim tables for cold starting, air intake temperature (IAT), engine coolant temperature (ECT), barometric pressure, battery voltage and more. With the additional software, the ECU can also log and graph data from these parameters in real time.
For the exhaust, Clark went with a tried-and-true part, FMF Racing’s slip-on Factory 4.1 RCT muffler/spark arrestor. We can vouch for the massive power gain of the FMF muffler since we recently slapped on a Husqvarna 501 test machine during our FMF Racing Factory 4.1 Dyno Test and were blown away by its performance. In fact, since it made 4.3 additional horsepower on that Husqvarna, it got us to thinking that maybe the 4.1 nomenclature in its model name is there for a reason. The Factory 4.1 RCT features FMF’s trademark Resonance Chamber Technology, which breeds a muffler core shape that alters the exhaust pressure wave for maximum power output while minimizing exhaust noise. The RCT is also shorter in overall length, which helps to tuck in better and be less susceptible to crash damage.
The only other noteworthy change to alter the power feel of the bike was a gearing change. Clark took a tooth off the countershaft sprocket, going from 14 teeth to 13 teeth to once again enhance the snappy feel at trailbike speeds. The 13/52 gearing and O-ring chain are from Supersprox.
DirtBikes.com test rider Nick Stover was on hand to swing a leg over our KTM project bike and give us his feedback. After busting around on the off-road trails inside Cahuilla Creek MX Park for the better part of two hours, Stover came back with a smile on his face.
“You can’t say anything bad about the KTM 350 EXC engine to start with, but the changes that are made are serious improvements,” Stover said. “It’s just awesome everywhere. The overall power delivery doesn’t feel any different than the stock bike except for feeling snappy right off the bottom. Otherwise it just feels like a stock bike with a lot more bark everywhere in the rev range. The 350 is such a fun engine, but this one takes that to the extreme, not because it feels any racier than before but because it’s just a lot easier to ride with the additional power on tap.”
While the KTM’s stock WP Xplor fork and PDS shock are also very competent, Clark went ahead and fiddled with the suspension anyway, enlisting a company that might be as synonymous with WP as others, Factory Connection.
“Factory Connection is known as the Honda suspension guys, but they really know how to do magic to the WP explore and PDS shock,” Clark said.
Factory Connection set up the KTM fork with .45 KG/mm springs and set the oil level at 100mm in the fork tubes. The low-speed rebound was set at 12 clicks out and the high-speed rebound was set at 10 clicks out. The fork height is set at 2mm above the top of the triple clamp. Out back, Factory Connection dialed-in the shock to balance with the fork.
With the mods, the KTM suspension is able to tackle whatever nasty terrain comes it way. Stover bounced through rocks and slithered through sand on Cahuilla’s off-road trails before heading out onto the motocross track to burn a few laps. Afterward, he gave the Factory Connection suspension upgrade high marks.
“It’s really controlled,” Stover said of the suspension action. “It’s clearly set up more for trail riding than moto. On the track, it was a little on the soft side, but it was still pretty good. Out on the trail, though, it’s really plush, especially in low-speed stuff. It doesn’t deflect or bounce around at all. They [Factory Connection] did a good job on it.”
The rest of the KTM is modified with a host of parts from the aftermarket companies that partner with Clark on his builds. For more range, Clark added an IMS Products fuel tank that swells fuel capacity to 2.6 gallons. Cycra Racing supplied a complete new plastic kit along with its Full Armor skid plate and Ultra Pro-Bend full wrap-around hand guards. For added protection on the lower frame and to keep the machine looking new, Clark also went with a set of KTM Hard Parts orange frame guards.
Even more protection comes from various suppliers. Bullet Proof Designs’s radiator braces and rear swingarm guard protect vital components from being thrashed by bushes and rocks while a TM Designworks chain guide is stronger than the stock chain guide.
The stock wheels have also been replaced by a host of Tusk Off-Road’s durable and relatively economical wheel sets wrapped in Dunlop AT-81 tires. The stock KTM brakes are held in place via a Tusk brake bolt kit, with the rear disc receiving added protection from a Tusk shark fin brake rotor guard. A Tusk sprocket bolt kit is also used. The only other Tusk item is a lightweight Lithium-ion battery that saves weight while also supplying plenty of juice for the KTM electric starter.
To provide better ergonomics, the stock handlebars are replaced by Renthal 604 Fat Bars and Tacky grips. On the throttle side, a Motion Pro Titan throttle tube also does away with the stock KTM part. Down low, Scar Racing titanium footpegs shave weight and provide an aggressive tooth pattern for better boot traction when riding.
Of course, throwing all of these cool parts on a bike with OEM graphics wouldn’t do much to deliver the message that this KTM is a cut above a stocker, so Clark called on DeCal Works to wrap the 350 E-XCF with a Semi-Custom graphics kit and pre-printed number plate backgrounds. Topping it all off is a Custom Cool seat cover from the folks at Moto Seat.
What you end up with is a KTM 350 E-XCF that offers more power, better suspension and a lot of neat components that can go just about anywhere and look good doing it. If you’re interested in any of the parts found on this bike, we’ve highlighted them below along with the links to their respective manufacturers.
FMF KTM 350 EXC-F Parts List
Two-stroke air filter cage
Orange frame guards 79003094000EB
FMF Racing www.fmfracing.com 310-631-4363
Slip on 4.1
Rear Stealth Sprocket 52T
Front Sprocket 13T stock is 14T
Vortex X-10 ECU
Oversized Fuel tank
Ultra Pro-Bend Full Wrap Around hand guards
Full Plastic kit
Full Armor Skid Plate
Two-stage Air Filter
High pressure radiator cap
Formed Silicone Coolant hoses
Moto Seat www.motoseat.com 951-258-5229
Custom Cool seat cover
Hinson Clutch Components www.hinsonracing.com 909-946-2942
Fibers, steels, springs and Outer Cover kit
Full Inner hub pressure plate kit
Stock front and Rear rotors
Complete Wheel set
Brake bolt kit
Sprocket Bolts kit
Lightweight Battery Lithium battery
Rear brake rotor guard (shark fin)
AT81 front 90/90-21
AT81 rear 120/90-18
Factory Connection www.factoryconnection.com 800-221-7560
Suspension set up
Bullet Proof designs www.bulletproofdesigns.com 816-695-3784
Rear Swing arm guard
Semi-Custom Graphics kit
Pre printed number plates backgrounds
Motion Pro www.motionpro.com 650-594-9600
Titan throttle tube
Rear Chain Guide
604 Fat Bars