We’re not rebels, just simple dirt idiots screaming for the bossest, nastiest and stealthiest dirt machine that is just road legal enough not to get shot. KTM has rocked the DS world this year with their very potent 350 and 500EXC machines. Both are new—from the engine, to the frame, to the fit, to the feel, to the handling and to the bump-absorption qualities. As for bone-stock street-legal dirt machines go, they are the best of the best. Having said that, we absolutely could not leave well enough alone and hunted down a reputable gear head with a penchant for pushing the limits. A couple of months ago, we tested a BestDual 500EXC; it was a machine that went from solid and fun to missile with an attitude. This month, we’re testing their sculpted and tuned 350EXC, a machine that can benefit from a little charge of meanness and some handling mods that just might transform this wagon into the best tight-trails machine on the block.
Note: In California, all engine and exhaust mods take this machine to non-street-legal status.
The 350 needs a gearing change to 14-50. You’ll need to install a longer chain ( installed an RK O-ringer) along with a 50-tooth Supersprox sprocket. The bike will still cruise the highway (it’s pushing pretty hard at 65 mph) if needed, but now it will have good gear spacing and acceleration for off-road.’s next step was to block off the exhaust air-valve hose to get rid of the deceleration popping. (Go to their website for a good visual.) This is a dirt-only fix that helps clean up the bottom power and do away with the off-power lean pops.
A No Loss throttle body really unleashed the potential of the 350 engine. The stocker is really soft down low, forcing a rev-it-and-peg-it mode of operation. There is not enough roll-on to allow for decent short-shifting and carrying taller gears through tough and technical sections. The 39mm No Loss unit uses new air valves that alter the air/fuel ratio to suit the 350’s powerband at different throttle positions. Since the computers are kept from making changes to the fuel, you can only manipulate the airflow to get the best ratio at different throttle positions. The big change in personality comes in an aggressive bottom-to-mid snort that the stocker simply does not have in its DNA. On the 500, it was a bit much for us; on the 350, it’s wicked good.
They mate the new throttle body to an FMF exhaust, an internally ceramic-coated MegaBomb (unique to and the 4.1 RCT rear system that has a spark arrestor and quiet insert. This union blossoms as the softly mannered, high-revving stocker wakes up with a ’tude, snaps and snarls down low, and has a very potent middle meat to the powerband. All in all, it’s a strong off-road performer.
One trip at speed will reveal that the wheels need to be balanced and the amount of weight to add is 3 ounces to the front wheel and 3.75 to the rear.
The exhaust air-intake tube still needs to be blocked to fix the pop or backfire upon decel, but on the 350, the tube is on the shifter side.
The stock tires come with 35 psi in them, so lower it to between 12 and 15 psi, depending on what you’re doing. The tubes are just light-duty tubes, so you’ll want to switch to heavy-duty ones before hitting the rocks.
A new fix in the basic category is modifying the fuel-tank breather line, especially crucial if you top off the tank and do any vertical up or down trailing. The reason it needs to be modified is that it has a gasoline-fume-purge system on it for emissions. Basically, this sucks the fumes out of the tank through the vent line, but also sucks the gas into the system if the tank is near full and the bike is pointed up or down enough to where the gas can run into the line.  When the purge system gets too much fuel in it, the bike will stall. You can drain the purge system, or if you are out on the trail, just pull the line off the gas cap and it will start to run again. You can modify it later. Note: this is not a street-legal modification.
Another new fix is to lube the gas cap. When you press the orange top of the cap, three orange plastic prongs release and you can twist the cap off. You’ll have to spray some lube inside those little tabs and smear some grease around the seal before you can get the cap off because it’s dry and sticky. fit the 350 with a one-step-stiffer fork and shock springs (going to .46 up front and a 4.2 spring on the rear). This is an important mod for all the faster guys and anyone over a buck eighty-five. They then fit Unshocks (flat-needle bearings) on top of the fork springs. Since springs are wound like screws, when they compress, they automatically want to twist. When the ends are held and at least one side can’t move freely, there is a little binding. It isn’t too bad on the EXC with the nylon spacers on top of the springs, but the bearing makes it even better. What you get is a little straighter tracking on the front end and more suppleness over the little stuff.
We’re loving the KTM EXC, and we have to tell you, BestDualSport makes them seriously meaty, better handling and more fun to ride. These guys love to tinker. Their website gives you good how-to-do-it info and photos, and their performance products and partners all offer goods that make a difference. In the end, it’s all good; they just make it smile and bark more like a big dog should.


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