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WHAT IS IT? Dick’s Racing progressively bores out the stock KTM 250SX two-stroke carb from 36mm to 39mm, installs the creative Intelajet system by Thunder Products, cuts the slide and installs a Thunder Products Quad Flow Wing. These mods work on the 2017 KTM and Husky two-stroke Mikuni carbs. Obviously, it also works on Keihin carbs.
WHAT’S IT COST? $585.00 (complete) or $275.00 (Intelajet installed), $150.00 (taper bored), $150 (Quad Flow Wing installed), $10.00 (cut slide).
CONTACT? www.dicksracing.com or (916) 705-3193; Thunder Products, www.thunderproducts.com or (320) 597-2700.
WHAT STANDS OUT? Here’s a list of things that stand out with Dick’s Racing’s 2017 KTM/Husky Mikuni carb mod.
(1) Stock KTM carb. For over a decade KTM two-strokes came with Keihin carbs, but for 2017, KTM (and sibling Husqvarna) switched to 38mm Mikuni TMX carbs. This wasn’t a popular change with KTM racers. KTM owners had struggled through several bad years jetting the Keihins before they got it right at the factory. The more finicky Mikuni was going to make all that knowledge obsolete. The MXA wrecking crew actually quit running our pre-mix at 40:1 and switched it to 60:1 at the urging of the KTM factory mechanics. It did help.
(2) Taper bore. Dick’s Racing taper-bores the 38mm Mikuni from 38mm to 42mm at the end. Tapering the carb’s bore allows the Mikuni to work like a 38mm carb below one-third throttle but a big carb above that.
(3) Intelajet. Intelajet is the two-stroke equivalent of Kawasaki’s dual-fuel injection nozzles. As air velocity increases, excess fuel is sucked directly from the float bowl to a secondary emulsion tube upstream from the main jet. At high rpm, this extra stream of atomized fuel enters the carb as a fine mist. The amount of fuel coming through the emulsion tube can be controlled by an air-bleed dial that’s accessible to the rider.
Looking down the bore, you can see the Quad Flow Wing and the Intellajet’s emulsion tube. The winglet straightens out the air flow, while the emulsion tube delivers a mist of fuel when the air velocity is fast enough to suck fuel directly from the float bowl. The blue tube goes to the float bowl and the clear tube go to the air control dial.
(4) Quad Flow Wing. Intake tract winglets take tumbled air and smooth it out to reduce drag at the air’s boundary layer. Reduced surface friction equalizes the pressure gradient and increases air velocity. The Quad Flow Torque Wing is unique in that it mounts on the cylinder side of the carb’s Venturi instead of the airbox side. Why? Because it wants to straighten out the air as it exits the carb.
(5) Slide. Raising the cutaway arch of the Mikuni slide causes more air to flow through the carb’s venturi at low throttle settings, creating a slightly leaner mixture at idle and a crisper transition into the midrange.
The Intellajet dial meters the air through the emulsion tube. Clockwise is richer and counter-clockwise is leaner.
(6) Performance. By increasing air velocity and adding a secondary fuel source, MXA was able to drop four main jet sizes on the 38mm Mikuni. We got snappier throttle response at half throttle and a big boost in top-end power when the atomized fuel joined the party. The gain in top-end power and over-rev was immediately noticeable to every MXA test rider. But, it took some fiddling with the air screw and Intellajet dial to find the perfect mixture.
WHAT’S THE SQUAWK? Combining every carburetor trick into one carb increases the power but also the price tag.
MXA RATING: If you’re looking for the last bit of extra oomph from your 2017 250SX or TC250 two-stroke, this is where you’ll find it.