Sad but true: The KTM 350SX-F will never win a motocross shootout. Why not? It would have to go through KTM’s own 450SX to get there, and then there are four other 450s that are faster and about the same weight. When you line up a bunch of test riders who are on top of their games, none are going to choose a bike that give them a disadvantage before the gate drops.
That doesn’t change the fact that the KTM 350SX-F is probably a better race bike for almost everyone, including you. Forgive us, but you’re probably not at the peak of your riding career. We can’t say this for sure, but we’re guessing you’ve been fitter at some point in the past—maybe you could bench-press a little more and weighed a little less. That’s where the KTM 350SX-F is at its best—when you’re not. It’s easier to ride and less intimidating than a big brute. That’s why we decided to build up our 350 test bike, making it an MX/off-road crossbreed for the average rider, but with just as much care and detail as if it were for a top pro.
Brandon Petersen and Justin Lewis recently formed AHM Factory Services, and we became aware of their work through Justin Jones. He uses them to prep his WORCS number three Bonanza Plumbing KTM, and we figured anything that could survive a two-hour WORCS race at pro speed would be adequate for vet-class racing in the real world. What we didn’t expect was that Brandon and Justin would take the project and go so far over the top. You need to understand the nature of most magazine project bikes to appreciate this. They generally fall into two categories: either they are the ridden-into-dust adopted bikes of our staff, which have been tested until they barely move under their own power, or they are glitz-and-gleam show bikes built mostly for visual appeal. This particular bike had both elements. It was tested and ridden hard, but the amount of detailing and attention it received was on par with a display bike that was going on tour. It was a real bike that just happened to look really good.
First, the frame was powder-coated in the same orange shade as the KTM 450SX-F Factory Edition. It got Acerbis plastics and Dirt Digits graphics, and then the real work began. As is always the case with KTM motocross bikes, the most important single factor was suspension. In the rear, KTM uses pretty much the same compression valve stack in all its motocross bikes. It’s a single-stage stack that ends up being stiff initially and soft at the end. Justin Lewis is a veteran from RG-3 and has seen WP shocks evolve over the years. At this stage, the quality and sophistication are equal to anything in the world, but they still have a very Euro-oriented feel. They’re made, quite simply, for faster tracks with more rolling whoops. Out here we find more chop, and a bike that’s scheduled for off-road riding needs to be softened up initially. AHM installed a new multi-stage compression stack. It was softer than stock but still allowed them to use the stock spring for a 185-pound rider, which was a big savings. The WP fork is the closed-cartridge version, which is one of three completely different forks found on KTMs this year and the most motocross-oriented. It was re-valved softer for off-road and, like the rear shock, was able to retain the stock springs.
Justin Jones got his two cents in. He recommended reducing the triple-clamp offset from 22mm to 20. We used XTrig clamps for this and got the additional benefit of the Progressive Handlebar Damping System, which is much more precise than traditional rubber-mounted bars. The clamps only allow vertical movement of the bars, so there can’t be any bar-twisting in a tip-over. Xtrig also makes one of the coolest preload adjusters on the market. With most bikes, you set the preload twice: once when you get the bike and once after the holidays, when you’ve gained 15 pounds. But with test bikes, the preload is constantly being changed up and down with each rider, and it takes a toll on the trashy little WP plastic adjuster. The Xtrig adjuster allows you to change the preload with an 8mm T-handle. The only problem is that you have to remove the top clevis of the WP shock for installation.
As for the motor, we had to walk a fine line. After all, the very reason we love the 350 is because it isn’t a 450. There was talk of a big-bore kit, but that was nixed early. We love the 350’s powerband, so it received mild head porting and a Pro Circuit T6 pipe. The clutch on the SX still uses coil springs, whereas the XC off-road models use a diaphragm spring. It was swapped out for the Hinson clutch, just for feel and durability.
There were three areas that were addressed to give the bike an off-road slant. First was the tank. IMS provided a 3.1-gallon tank that gave the bike real range. The bike also got Acerbis handguards and ARC Memlon unbreakable levers. The motocross version of the 350 doesn’t come stock with a fan to keep the motor cool at slow speeds, but Dirt Tricks makes one. The bolt-on kit has an on/off switch that can be mounted anywhere.
Then there’s the wheel issue. As usual, there’s a problem with the rubber. One off-road ride will roach regular motocross tires, so the best way to have a double-use bike is to have two sets of wheels. The stockers were set aside for motocross, and a set of Talon/DID Dirt Star wheels from Dubya were set up for off-road. The rear was an 18-incher, and both ends got STI Tech 2 MXC tires with STI Extreme Duty tubes, which are almost flat-proof.
Petersen went so crazy detailing the bike and making it beautiful that we almost felt guilty about riding it. Almost. The 350 is one sweet bike. In the suspension department, it got exactly what it needed. It’s cushy, but you can still go full speed on a motocross track without any hard clanks or clunks. Even hard-core motocross riders liked it better than stock. It has an initial cush that the KTM really needs. Off-road, the bike was excellent, even on trails that were essentially first-gear slow.
The slight steering geometry change brought on by the reduction in offset was met with mixed reviews. Justin Jones loved it because it gave the KTM a Honda-like feel that he has always liked. Less-sensitive riders didn’t notice much. Reductions in offset result in an increase in trail, which is a very complicated subject. In this case, it made the steering feel lighter.
The bike is being ridden, tested and modified every week. The picture is always changing, but the bottom line is that we started with a truly great motorcycle and then personalized it, gave it more focus and made it even better. We wish all projects worked out this well.

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