KTM has made 50-horsepower 250cc engines in the past, but this engine focuses on midrange hit and torque.
Husqvarna airbox. The hit was made more manageable,
and the powerband revved out further. All it takes is a strip
of duct tape and one minute of your time.
( 3) Unplug the secret wire. Unlike the KTM four-strokes, the KTM two-strokes do not come with an adjustable map switch; but, what few people know is that they
do have two maps. The stock map is the aggressive map,
and it comes installed in the bike. There is a mellow map,
but it is hidden under the gas tank. Look under the tank,
just in front of the cylinder head, and you will see a wire
hanging down with a white male/female connector. If you
unplug that connector, you will activate the mellow map.
Q: WHAT IS THE MOST IMPORTANT
CHANGE THAT EVERY 250SX RACER SHOULD
A: Stock gearing on the 250SX is 14/50. The MXA test
riders had issues with the lack of top-end over-rev on the
2018 KTM 250SX. Plus, the gear ratios seemed a little off
from gear to gear. We killed two birds with one sprocket
by gearing the 250SX taller. We switched from the stock
50-tooth rear sprocket to a taller 49-tooth sprocket. This
smoothed out the power, lengthened the gap between
gears and made the KTM 250SX feel like it pulled higher
into the rpm range. It didn’t actually make its power at a
higher rpm, but it took longer for the gears to get to the
peak horsepower, which was at a fairly low 8200 rpm.
Q: WHAT IS THE SECOND-MOST
IMPORTANT CHANGE THAT EVERY 250SX
RACER SHOULD MAKE?
A: Last year, when KTM switched from Keihin PWKs
to Mikuni TMXs, we struggled with the jetting. It became
a weekly ritual. Eventually, we sought help from JD Jetting
and got the bike close. But, shockingly, we found an easier
way to fix our jetting problems.
In the KTM 250SX owner’s manual, it says to run a gas-to-oil ratio of 60:1. We thought it was a typo and ignored
it. But, the more we struggled with the Mikuni jetting, the
more the KTM factory mechanics asked us to switch from
Maxima at 40:1 to Maxima at 60:1. Finally, we folded and
put the stock jetting back in our bike and sent three test
riders out on 40:1 fuel. Then, we switched the bikes to
60:1 and—voila!—the 60:1 ratio was better. To make 60:1
premix, you add 10. 7 ounces of oil to 5 gallons of gas. The
only jetting change we made was to go to a bigger 55 pilot
(and then we used the air screw to fine tune the pilot).
Q: HOW DOES THE 2018 KTM 250 HANDLE?
A: The MXA wrecking crew loves the neutral handling of KTM’s 250SXF, 350SXF and 450SXF four-strokes.
So, imagine how close to happy land we are on a 212-pound
two-stroke that isn’t bound by the front-wheel steering
rules of the typical thumper. KTM’s chromoly steel chassis
is exponentially better with a two-stroke engine than it is
with a four-stroke. Lines that you could only watch go by