The powers that be in our sport have forsaken the 125 two-stroke. They
made it obsolete with rules that
favored four-strokes by doubling
the thumper’s displacement. But,
the 125 is making a comeback.
Not with a bureaucratic stamp of
approval, but with homegrown
enthusiasm for what motorcycle
riding is supposed to be about—
Nothing can match the sound of
a 125cc two-stroke at full-tilt boogie. Every shift snaps like a crack
of lightning as the rider dances
on the edge of the power curve.
The tension of the rider trying to
keep it on the pipe while using
maximum body English to keep
momentum up is visible. Best of
all, if you rode your 125 perfectly
for one lap, you probably felt like
a king, because you were pretty
sure that you couldn’t do it for
two laps. Going fast on a 125 is
like balancing on a high-wire in
Swedish clogs—it can be done, but
you pay for any mistakes.
Most riders from the two-stroke
era have fond memories of
racing a 125. There is something
so visceral about going flat out;
the experience sticks in your gut
for a lifetime. The MXA wrecking
crew wanted to feel those sensations again. So, we decided to
build a full-race 2015 KTM 150SX.
Why didn’t we build a true-to-life
125? Because we had a 150SX
sitting in the workshop, and logic
told us that a bird in hand was
better than two in the bush. Plus,
the extra 25cc would come in
handy on jump faces.
It was not our intent to build
a show-stopper bike. Everybody
loves to look at garage queens,
but when it comes to the dirty
world of racing, we favor performance over exotica. And, we
didn’t want to break the bank,
which is so unlike us. We wanted
a workhorse, not a unicorn.
Here’s how we did it.
(1) Cylinder head. We got
an adjustable VHM cylinder head
from TM importer Ralf Schmidt.
This Dutch-made cylinder head
has improved water ducts and
provides better heat transfer.
The combustion chamber can be
changed for different compression
ratios and squish zones. When
we ran race fuel, we used the
high-compression head, and for
practicing and play riding, we
used the low-compression head