Batteries included: The only two pieces that didn’t come from the KTM parts shelf were the exhaust pipe and flywheel weight.
gas tank; 18-inch rear wheel; kickstand; heavier flywheel;
soft enduro suspension; and electric starter. All nice
touches, but none of them add anything to the motocross
side of the package. Plus, the MXA wrecking crew spent
lots of time and money undoing all the great stuff that
KTM had done on the offroad side of the equation to turn
the bike into a motocross bike.
Q: WHY DO WE RECOMMEND STARTING
WITH A KTM 250SX?
A: Simple Simon. The 2014 KTM 250SX comes ready
for motocross. It has stiffer suspension; a smaller, 1.98-
gallon gas tank; a close-ratio, five-speed gearbox; 19-inch
rear wheel and lighter overall weight. It also doesn’t have
the unnecessary kickstand or electric starter.
Sadly, the one thing that the 250SX doesn’t have that
the 300XC does have is the 300cc engine. But, that is
Q: HOW DO YOU TURN A KTM 250SX INTO A
A: MXA turned its 250SX into a 300SX by going to
the bank and withdrawing $950 to buy KTM’s PowerParts
300cc cylinder kit.
The PowerParts 300 kit includes a new cylinder, head,
piston, rings, wrist pin, gaskets, clips, O-rings, power-valve
parts and black box. Every part comes directly out of the
KTM parts bin and is high quality.
There are two PowerParts 300cc kits: enduro and
motocross. We have experience with the 300cc enduro
kit also, and with its lower compression and a different
black-box map, it is smoother and easier to ride. But, for
our purposes, we opted for the motocross version.
Q: HOW HARD IS THE 300 KIT TO INSTALL
ON A KTM 250SX?
A: For the most part, it is no more difficult than
doing a top-end job. You remove your old 250cc top
end intact. You won’t be using any of the top-end
parts, so they don’t have to be disassembled after they
are removed. This is cool, because it means that you
will have a spare top-end (head, cylinder, piston, rings,
power valve and black box) sitting on the shelf ready to
go should you need it or want to sell your trusty KTM
250SX and buy a new one to put the 300 kit on.
Q: WHAT IS THE MOST CRITICAL STEP IN
TURNING A 250SX INTO A 300SX?
A: Since the 300cc cylinder has a 72mm bore, the
250 power valve will not fit into the big jug. This is
good, because it allows you to keep your old 250cc
top-end in ready-to-use condition. KTM supplies an
upsized flapper valve and power-valve mechanism with
the 300 kit, but it has to be assembled. Luckily, you
will have your old 250cc cylinder to look at if you get
confused, but for anyone with a modicum of mechanical
skill, the power-valve mechanism goes together without
Of course, you have to adjust the power-valve height
by adjusting the linkage mechanism. We did this by
2014 KTM 300SX