The 300 kit is available from KTM Power Parts and
sells for a fairly hefty $949.99. It consists of a new cylinder, head, ignition box, piston/rings/circlips, gaskets, and
power-valve flapper. So, actually, the price of admission
is acceptable, especially when you consider that just purchasing a new 250SX cylinder would set you back a little
under 400 bucks. Our bike came fit with a Pro Circuit pipe
and silencer, the muffler being the straight-through moto
The installation of the kit is straightforward, though poor
instructions hamper the process. Jetting changes came
via the Intelajet. It adds a separate air-fuel delivery device
that features external adjustability for improved response
and fuel mileage. The Intelajet allows you to control
fuel flow externally by rotating the knob in the appropriate direction—richer or leaner. The new KTM 300 piston
was shelved in favor of a high-compression Wiseco unit.
Remember, one of the goals with this machine was to
make it competitive with a 450!
THE TRACK TEST
This 300SX will make your eyes water and lips curl. It
hits with a ferocity that is almost alarming, and since we
were used to the high-torque and flywheel-heavy zest of
a 450, this dude took some getting use to. Thankfully, it
wasn’t just our older pilots who were shell-shocked. Justin
Jones praised the powerband, saying that it was nice to
get on something with an explosion factor: “The power is
really amazing! It comes on quick and hard and snaps in
the direction desired, while still having a hard-grunt bottom
end similar to a 500. Easy to ride yet still powerful—just
like a lightweight two-stroke should be.” It feels like it
goes flat a little early, so we plan to adjust the power-valve
spring tension after having gone slightly richer with the
Intelajet device, looking to get rid of some of the tinniness
and abrupt hit. Richer jetting helps thicken the feel of the
power, and this helps control by slowing down the hit.
Overall, the only gripe with the powerband was an early
sign-off and maybe too much hit down low. We can always
tune for more subtle response, but starting with too much
is far more acceptable than trying to make more.
Suspension-wise, Pro Circuit continues to make us
happy. Two of our beanpole testers felt that the machine
was over-sprung, but the bigger vets praised the fork’s
initial freedom and its ability to “stay up” under duress and
not dive. The combo of properly sprung suspension and
the right sag (105mm) helped keep the machine planted
and fairly stable and improved cornering over stock.
Justin Jones is our pro tester and a regular on the podium of the WORCS Pro division.
—This engine package is unbeatable for a mid-size two-
stroke. Even with carburetors almost becoming a thing of
the past, the SX never even hinted at having the slightest
—The gearing was good for your average motocross
track, but if you were racing anything a smidgen faster, I’d
go smaller out back, since I seemed to be shifting into fifth
more than I like to.
Here’s the 300 conversion kit from KTM’s Power Parts division.
Pro Circuit performed their magic with the suspension, dialing it in for a big-guy Vet rider with new valving and a stiffer
spring rate out back. www.procircuit.com
Intelajet provided a means for fuel-flow adjustability via their
Dial-A-Jet. Dial-A-Jet is like a power jet, but it has air bleed,
so instead of feeding raw fuel like a power jet, the device
meters the air and mixes it with the fuel in a chamber, delivering a pre-atomized fuel mixture into the center of the carb