That’s living: You haven’t lived until you’ve rocketed out of a corner on a 52-horsepower two-stroke. Things happen fast.
Q: WHAT JETTING DID WE RUN?
A: KTM has made last year’s richer N1EH needle
stock, made the N1EI the optional lean needle, and
added an even richer optional N1EG needle. KTM also
raised the needle one clip position (from the 3rd to the
4th clip from the top). If you ride in cool weather,
consider going to a 160 mainjet and N1EG needle. We
also swapped out the stock 42 pilot jet for the leaner 40.
Here are MXA’s recommended jetting specs for the
36mm Keihin PWK carb (when changed, stock specs are
Pilot: 40 ( 42)
Clip: 4th clip from top (3rd from top)
Air screw: 1-1/2 turns out
Notes: We found the stock 250SX jetting to be in the
ballpark, but as with all of our two-strokes, we spiced up
our 91-octane pump gas with a splash of VP C- 12 just to
ensure fuel quality.
Q: HOW FAST IS THE 2014 KTM 300SX?
A: The one thing we didn’t want was lots of power
mated to a brutal hit and an arm-jerking rush. Okay, our
former AMA National test riders did want that, but the
mere-mortal test riders found that the smoother we made
the powerband the more effectively they could use the
added horsepower and torque, which went up from
32. 19 foot-pounds to 34. 31 foot-pounds with the Pro
Circuit 300XC pipe.
Don’t get too enamored with building a fire-breathing
KTM 300SX. You don’t have to. With just the addition of
the PowerParts 300 cylinder kit, the Pro Circuit
300XC pipe and the R-304 shorty silencer, we gained
2.0 horsepower at 5000 rpm, 2. 7 horsepower at 6000
rpm, 5. 5 horsepower at 7000 rpm, 2. 4 horsepower at
8000 rpm and 2. 2 horsepower at peak.
It’s no secret that two-strokes are cheaper to buy,
less expensive to maintain, simpler to work on, 20
pounds lighter and more powerful per cubic centimeter
than four-strokes. In fact, it was possible for us to get our
KTM 300SX kit bike to make more peak horsepower
than a 2014 Honda CRF450.
Q: WHAT DID IT COST?
A: To replicate our 300SX engine package, it would
cost $1440. That is $950 for the PowerParts kit, $250 for
the exhaust pipe, $120 for the silencer and $120 for the
flywheel weight. The total cost, including a brand-new
2014 KTM 250SX, would be $8540. Now, you might be
tempted to think that it would be cheaper to buy the
$8500 KTM 300XC, but to duplicate our 250SX-based
machine, you would need to have the forks and shock
re-valved, buy the smaller gas tank, relace the wheels to
19-inchers, and you would still have to buy the exhaust
parts. Even then, you would be hampered by an extra
15 pounds of weight and a wide-ratio, six-speed gearbox
that doesn’t work very well in motocross.
Q: WHAT DO WE REALLY THINK?
A: If you own a KTM 250SX that you’d like to get
more power out of (or just freshen up), we’d seriously
consider turning it into a 300SX. It will make more horsepower than any mod you could ever make to your stock
250cc engine, and you will still come in under budget. ❑