MR. KNOW IT ALL MR. KNOW IT ALL
HUH? MORE OIL MEANS
Dear Mr. Know-It-All,
Most respectful ambassador to
the moto brain, I just bought a new
2015 KTM 300 XCW. Please don’t
tell my wife! Anyhow, as I left the
service department after prep, the
service manager told me that it had
gas with an oil ratio of 32:1 in it right
now and to run that for two tanks
until it was broken in. Then he said to
switch to 60:1, as that was what was
recommended. The thing is, it runs
pretty well with the 32:1, and knowing
enough to know that 60:1 will make it
run quite a bit richer (less oil = more
gas to the same amount of incoming
air = richer) and considering the fact
that we are going into summer, would
you do this?
Loving my 300 in Idaho!
Via the Internet
You know, you have to be one of
the elite among our bevy of readers.
Not only have you acknowledged
my superior intellectual power from
the start, but you have also basically
answered your own question. I will,
however, elaborate for the others.
In the world of two-stroke jetting,
other than the actual brass jets them-
selves, there are three factors, outside
of deteriorating engine condition, that
affect whether the bike is running rich
or lean. The three factors are air temperature, elevation and the ratio of fuel
to oil you choose to run.
You can’t control the air temperature or elevation, but you can control
the fuel-to-oil ratio and the jet size.
Before we start with the others, let’s
make it clear, once again, that higher
elevation equals less air, and therefore
the bike runs richer. Higher temperatures also mean less air (thinner), so,
again, it runs richer.
A two-stroke engine actually has
primary and secondary compression.
In the world of jetting, I consider the
fuel-to-oil ratio the primary jetting and
the jets secondary. This is because
the fuel-to-oil ratio fed to the carb not
only affects all jetting ranges, but also
determines it first before it gets to the
jets. A ratio of 20:1, which is 6 ounces
of oil in a gallon of gas, will make the
bike run noticeably leaner than a ratio
of 40:1, which is 4 ounces of oil to a
Personally (and I think other really
intelligent people agree), I think it
makes sense to mix a gallon of gas at,
say, 20:1, 32:1 and 40:1 and test to
see which blend makes your bike run
better. It’s an easy way to determine
which ratio is best for your style of rid-
ing and allows for easy changes when
you head up to higher elevation and
don’t want to re-jet.
Also, at higher elevations and in the
warmer temperatures of summer, you
may not be able to get a small enough
pilot jet in the 300 for it to run well at
60:1, since the pilot jets are close to
the end of the available range.
Compiled, researched and answered by
our own Mr. Wizard, Dave Simon.
Next, it’s jet time. Most people
know that you can remove the top cap
with the slide and be able to turn the
carb enough to get to the jets without
taking the carb off. The hexagonal
one on the right is the main jet, which
controls fuel at mainly mid-wide-open
throttle. The middle one is the pilot
jet, which controls fuel at low throttle
openings, and the one on the left is a
special jet for fuel control when starting the bike. It’s new and is one of the
reasons KTMs start easily. It shouldn’t
need to be changed.
Next, you have the slide and needle,
with the clip in the set of grooves.
Moving the clip up or down is the
most common change people make,
making the bike run richer or leaner,
from about 1/4 throttle to 3/4 throttle.
Moving the clip up makes the bike run
leaner, and moving it down makes the
bike run richer.
Also, don’t forget that two-strokes
have an air-adjustment screw found
on the airbox side of the slide. Turning
it out makes the bike leaner just off
idle, and turning it in makes it richer.
It’s an easy way to dial in response at