2018 KTM 250 XC-W TPI
FIRST TEST
P120
EXPLAIN
INJECTION
The 2018 KTM 250 XC-W TPI two-
stroke is indeed fuel injected, but it
isn't fuel injected the same way your
four-stroke is. The overall architec-
ture of the KTM two-stroke engine
hasn't changed except for the cyl-
inder, and that really didn't change
much. The core dimensions and
layout of the TPI cylinder are carried
over from the carbureted model,
but the new cylinder now features
two lateral domes holding the fuel
injectors that inject fuel into the rear
transfer ports. This downstream
injection provides excellent atomiza-
tion of the fuel with the up-stream-
ing air for a highly efficient combus-
tion. It also significantly reduces
loss of unburned fuel. The engine
management system's intake pres-
sure sensor is connected via a
small-diameter tube in the back of
the cylinder.
Replacing the Mikuni carburetor
is a newly developed 39mm throttle
body made by Dell'Orto, featuring
a butterfly valve controlled by twin
throttle cables. The throttle body
on the TPI two-stroke controls the
amount of air to the engine, fuel
does not pass through the throttle
body, only air. Intake air data is pro-
vided to the engine management
system by a throttle position sensor,
while an adjusting screw allows the
idle speed to be set. A cold-start
device is also provided, opening a
bypass to supply extra air.
THE TPI BIKES
IDLE DOWN
AND LUG
INCREDIBLY
LOW WITHOUT
A HICCUP OR
COUGH, EVEN
BETTER THAN
A PERFECTLY
JETTED CARB.
The only bummer
is that we have
to wait until after
summer to get
one.
