KTM 350 EXC | Dual Sport Surgery

Less Street, More Dirt

By Karel Kramer, Photography by Karel Kramer

The range of machinery in the dual-sport category is amazingly broad. KTM's 350 EXC is one of the cutting-edge models that are literally high-end off-road competition machines with minimal street equipment. So minimal that the weight difference between a competition-only KTM 350 XCF-W and the plated EXC model is approximately 6 pounds. For this project, we’ve taken a marginal streetbike and made it worse on pavement. We reduced the highway cruising speed and further limited the available pavement traction, but the dirt capability is vastly improved. Trust us, these mods will make sense to those who really want to take their dual-sports off road, or even racing.

There is no question that a single-cylinder, 350cc engine is fairly small for the American highway system, though the KTM is powerful for its size. Truth is, KTM made the 350 EXC street legal so it could connect one trail to another via roads (paved or not) where a plate is required. At least 95 percent of this bike’s use is on dirt. I wouldn’t ride it to the Rock Store or any other store unless I’m slipping away from trails for fuel, food or lodging.

Offsetting KTM’s inattention to street capability, it made no compromises in off-road suspension and chassis performance. As a result, the chassis is ready for all but high-level motocross, so we left the suspension and ergonomic set-up alone.

On the other hand, street gearing and tires compromise performance off road. The stock tires have the DOT numbers that make them street legal, but they are also European-spec enduro tires that are limited to tread blocks 13mm tall. The rear tire has tall sidewalls that make the back end bounce and wallow. Dunlop has plenty of DOT-legal tires that work fine on the pavement and in the dirt. Since we had so little street in mind, we opted for maximum off-road performance with Dunlop D952 tires.

That change alone made a big difference. The D952's outside diameter is smaller than stock, so it has the same effect as lowering the gearing. But that wasn’t enough. Stock gearing is 14/45, but the same bike in off-road form is geared 13/52. Most riders opt for 13/47 or 48, since that allows the use of the stock chain. We wanted optimal tight-trail performance, so we installed 13/50 Renthal sprockets encircled by an RK chain. The shorter 13/50 gearing really isn’t happy on the highway for any length of time, but for hardcore off-road this gearing allows tackling most obstacles in second, leaving first as an emergency save-your-butt gear.

Dave Simon at Best Dual Sport Bikes (www.bestdualsportbikes.com) offers everything you would want for the EXC. In fact, all the bolt-on parts here came from BDSB. The main reason to use BDSB is its Magic Mod replacement throttle body. It runs $125, and is available on an exchange basis. DBSB tweaks the throttle body to trick the CPU into providing more fuel and altered ignition timing, and the resultant increase in bottom-end power is amazing.Throttle response and performance is much better than stock. The “carburetion” is perfect at any elevation, and no matter how hard the bike is ridden.

BDSB combines the Magic Mod with an FMF spark arrestor/muffler and header pipe. The ceramic coating inside the header is a BDSB exclusive. The combination of the gearing, pipe and throttle body mods make for a bike that performs even better than the 350 XCF-W off-road competition model. The XCF-W is as clean as the EXC with the Magic Mod, but the FMF header adds bottom-end power and throttle response that the stock XCF-W can’t match.

As mentioned before, the gearing and tire changes hurt the KTM’s on-road capabilities, but the bike is crazy good once the pavement ends. One Arrowhead section of giant rock-slab climbs was packed with stuck Jeeps and riders on off-road competition bikes. The 350 slashed right through the section despite many of the best lines being blocked. The same area required much clutch abuse with the higher-geared stock bike. Slow, relentless rock-step switchbacks that were misery before were much easier on the modified bike.

Honestly, the performance is so good that I can’t think of an off-road race that I would hesitate to enter on this street-licensed bike. I wouldn’t even take the Doubletake mirror or turn signals off.

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