There is a reason that the KTM 350 is the most popular machine offered by the Austrian giant. It’s fast enough, easy to ride, doesn’t wear you out like a 500 and feels substantially lighter than a 500-—though in reality the weight difference is minimal. Even though our main off-road playground is Southern California’s high desert, where you’d think that a 500 would rule, we actually prefer the 350XCF-W. But the other reality is that we always welcome more power, and that was the jumping-off point for this story.

The folks at Cylinder Works sent us one of their 365 big-bore kits for the KTM 350XCF-W. It consists of a new cylinder, piston, rings, clips and gaskets. We worked with Best Dual Sport Bikes, asking for their help with the install and dialing in the injection numbers. We coaxed Dick’s Racing into helping with valving and springs for the suspension and several nice additions that improved the ride, the traction factor and the machine’s ability to conquer some tough terrain.




The evolution of the 350 has been aggressive since its introduction in 2011. This year the SX-F and XC-F have been on the receiving end of big improvements via the cases, piston, new rev limiter, intake and exhaust port changes, and an increase in horsepower from 48 to 54. The XCF-W line also received changes, though the machine has a heavier crank for additional chugging and is altogether softer throughout the power range. While we had no aspirations of reaching the SX-F’s numbers, we really wanted a kick in bottom performance in hopes of sparking roll-on and the ability to pull a higher gear.

The Cylinder Works’ KTM 365cc kit sells for $649.95, and you get a new cylinder, 2mm-larger Vertex piston and a Cometic gasket kit. The bolt-on kit changes the bore and stroke from 88mm by 57.5mm to 90mm by 57.5mm. In all honesty, it’s a very straightforward parts swap. According to Dave at Best Dual Sport Bikes, the cylinder walls were pretty dirty, so he used hot soapy water (believing it’s better than solvent for opening the pores) to get all of the dirt out. The installation was smooth. He set the squish-band clearance (the space between the top of the piston and the cylinder head) a little looser than the SX-F/XC-F numbers, which get the compression to 13.5. He brought it down to 13:1, and this made it good for pump gas. He wants between .040 inches and .060 inches of squish. You can use the stock KTM gaskets, not the Cometic gaskets that come in the kit, and that will make it .040 inches. You can add another base gasket to get .060 inches. Dave also mentioned that this is important on the XCF-W since the kit really was designed for the SX-F and XC-F, where the squish-band drama is not an issue. This brings up the fuel metering, which is a source of concern since the big-bore kit really needs a richer air/fuel scenario. BDSB offers their Magic Mod for the ECU, but they informed us that you can get the Euro map, and then the dealer can add the necessary fuel numbers.



We really have no issues with the stock KTM exhaust. The stainless header is strong, and the muffler is one of the quietest yet flowing stock cans on the market. Still, we tested an FMF MegaBomb and 4.1 rear can (with spark arrestor) and came away impressed. Just bolting on the MegaBomb header (we went stainless since it’s stronger and this is an off-road project) with the stock muffler improves both the bottom hit and lower midrange. This helped to maintain the quality quiet factor of the stock machine. Second, we fit on a 4.1 rear muffler. Yes, the decibel level picked up, but so did the power. We felt a strong gain from upper bottom all the way to peak, besides getting a nice weight savings.


To keep things running smooth and cool, we fit up a Trail Tech cooling fan system. This unit is wickedly well-made and fits perfectly on the inside of the right radiator. It is thermostatically controlled (kicks on at 190 degrees), and when we were in the tight, ugly stuff, it kicked on and stayed on for substantial periods of time. The install was straightforward, though you do have to remove the radiator. Then you fit on the new frame and fan and run the wiring harness back to the battery. Quick and dirty.

To mix things up a bit, we decided to bolt on new plastic (since the stock stuff was roached) and fit a whole Acerbis black plastic kit onto the machine. With the exception of the airbox (stock is white), all of the pieces fit up perfectly. With the airbox, just getting the stocker off was a nightmare. The wiring harnesses, battery, battery box, etc. have to be removed, and figuring out the order of removal was trial and error. Having some instructions would have helped. Realizing that we had to drill out and re-rivet the side panels’ female receptors felt like a National Treasure adventure. Still, we did it and it looks great. N-Style bellied up with a graphics kit, which really set off the look of the machine.

On top, we fit on some new Fasst Flexx bars (their Enduro 14-degree bend) that feature more real estate on each bar end for switches and handguards. We dropped the red/red elastomers (stock density) for yellow/red (one softer on the compression). This seemed to give the best off-road ride, though it might be a little too wallowy for the hard charger. Overall, every single tester loved this handlebar! The A’ME bolt-on full-waffle grips gave good feel, subtle flex through the ridges and strong traction. Again, a favorite. Enduro Engineering’s hand deflectors are also favorites, not only for their ease of installation but also for their durability and the protection they provide for a West Coast off-roader.

On the suspension front, we wanted to firm things up since the stock open-bath system is very cushy but divey and soft for faster terrain. The rear PDS system definitely needs a stiffer spring for our tonnage, along with some shim adjustments to get it to stay tall under speed loads. Dick’s Racing retrofitted both suspension ends and, possibly because we’ve been working with Dick for several decades, nailed it on the first try. It was stiffer, still plush (enough), and most definitely not wallowy and plunge-happy. All good here.

Rad Manufacturing set us up with a set of their Signature Series wheels. Gold USA machined billet hubs, powder-coated stainless steel spokes and Excel Takasago rims bristled with a high cool factor. Once we bolted on a Moose Racing front and rear rotor, fit some DP brake pads (better feel than stock), a Supersprox 52-tooth rear sprocket and a Renthal O-ring chain, we gained a spare set of wheels and our race setup was strong and effective. These wheels held up well. Up front, we fit a Dunlop AT 81 tire, liking its grip factor in intermediate terrain, and installed a Dunlop trials tire out back. Again, dry conditions morphing from hard to rock to loose made this rear grabber a total cheater. Out back, we did fit on an Enduro Engineering disc guard after wadding one rotor. The EE unit is machined out of billet and strong.

Some of our final steps were setup and personal-preference modifications. Webb is tall with gimpy knees, and he demands a tall saddle. SAR’s saddle is one of his favorites since it is 12mm taller and stiff. T. Webb also prefers Fastway Evolution Air footpegs; they have great bite and an adjustable height that we run in the low (roomier) position. One of the final mods was the addition of the Enduro Engineering skid plate. The unit is thick aluminum, fairly light, and offers strong protection for the cases and both sides of the engine.


Kudos to Cylinder Works and a big thanks to Dave at Best Dual Sport Bikes for his help. Our KTM 366XCF-W morphed from one of our favorite off-roaders into a total trail demon. We gained both bottom to mid power, with the roll-on department bulging nicely. And, interestingly enough, the machine pulled just about as long as stock and kept the chunk of power it gained. The FMF system really helped mid to top power, and overall the improvements targeted everything that we crave for out-there riding. It was more tractable and stronger and allowed for short-shifting. It lugged and chugged with far more of an appetite and still pulled long and hard. We geared it a little low (13/52), and this hurt our sixth-gear top speed, but it most definitely made for a killer second- and third-gear trail combo. We found little fault with this engine and recommend it to anyone and everyone who explores trail and has a taste for tough terrain.

All of our other modifications were also winners. The Fasst Flexx bar gets an off-road gold star. It removes some the trail jitters and is wonderful on long, demanding rides. The Rad Signature wheels proved strong and durable. The Dunlop AT 81 front is adequate for the terrain, while the trials rear not only gave great bite but softened the hit out back in boney rock zones. Also, thanks to STI for their super heavy-duty tubes. They are crucial when you run a low-psi trials tire. In the suspension division, Dick’s did their homework, improving the big-hit ability and ridding the suspension of the Dead Sea wallows.

Here’s the finale: we love this bike stock. Now it rocks. Plain and simple. o


Cylinder Works: www.cylinder-works .com 

FMF Racing: www.fmfracing.com

Best Dual Sport Bikes: Magic Mod

Rad Manufacturing: Signature Series wheels

Enduro Engineering: Hand deflectors, Skid plate

Fasst Company: Flexx bars

Dick’s Racing: Suspension mods

Dunlop: Tires

TM Designworks: Chainguide

Supersprox: Sprockets

Renthal: Chain

Fastway: Evo Air footpegs

Moose Racing: Rotor

DP Brakes

STI: Tubes

Motion Pro: Rim tape/Rim locks

SAR Racing: Complete Tall saddle

N-Style: Graphics kit

Acerbis: Complete plastic kit



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