User Manual

7
TUNING THE LOW-SPEED NEEDLE
The low-speed needle (also referred to as the idle mixture
or idle needle) should be set after you’re satisfied with
thehigh-speedneedlesetting.Afterachievingtheproper
operating temperature, make a couple of high-speed
passes and then reduce the engine throttle to the idle
position. Pinch the fuel line with your fingers close to the
carbfuelinletnipple.Iftheenginediesimmediately,the
low-speedneedleissettoolean.Iftherpm’sincrease
dramatically, the setting is too rich. The ideal setting
results in the rpm’s increasing just a slight amount after
pinching the fuel line.
MID-RANGE NEEDLE ADJUSTMENT
The mid-range adjustment screw adjusts the air/fuel
mixture at half throttle and can dramatically affect mid-
range throttle response. The factory setting will provide
a slightly rich mid-range. For a crisper leaner mid-range,
desirable on high traction tracks where maximum
acceleration is needed, turn the mid-range screw out
(counterclockwise) 1 full turn. To soften the mid-range
response (richer), turn the mid-range screw clockwise 1
full turn for a softer feel during acceleration, best suited
for low traction conditions.
Note: The mid-range adjustment screw and
low-speedneedleworkinunison.Anytimethe
mid-range adjustment screw is adjusted it will
be necessary to readjust the low-speed needle.
When turning the mid-range screw in (clockwise),
the low-speed needle will need to be backed out
(counterclockwise). When the mid-range screw
is backed out (counterclockwise), the low-speed
needle will need to be adjusted inward (clockwise).
IDLE SPEED ADJUSTMENT
The last setting to be made is the idle speed. Remember,
this adjustment should be made while the engine is
running at normal operating temperature.
1. Make sure the throttle trim is set so that the
carburetor is fully closed against the idle speed screw
when the trigger is in the neutral position. The best
way to assure that this setting is correct is by applying
thebrakesafterseveralhigh-speedruns.Afterthe
vehicle has stopped, release the trigger to the neural
position, the engine should not pick up rpm’s. When
the brakes are reapplied the rpm’s should not drop.
When the throttle trim is set correctly you should have
to apply a slight amount of forward throttle before
the rpm’s begin to rise from idle. This will ensure that
the throttle slide is resting against the idle adjustment
screw.
2. Turn the idle speed screw counterclockwise to reduce
the idle speed, or clockwise to increase it. When there
is a need to increase the idle speed, slightly open the
throttle position while doing so in order to keep the
idlescrewfromdamagingthecarburetorslide.Ideally,
the engine should idle just fast enough to be reliable.
Avoidanidlethatissettoohigh,asitwillcausethe
clutch mechanism to overheat and fail.
FINE-TUNING THE CARBURETOR
Daily changes in temperature and barometric pressure
mayrequireyoutoadjustyourcarburetorsneedles.Also
if you run your vehicle at a new location at a different
altitude, some carburetor adjustment may be needed.
When the weather is colder and the air density is higher,
you may need to richen the fuel mixture.
Conversely when the weather is warmer and the air
density is lower, you may need to lean the fuel mixture.
Remember to make small adjustments of 1 hour at a time.
Imaginetheslotintheneedleislikethehourhandona
clock.Adjustitasthoughyouweremovingthehourhand
from one hour to the next or previous one.
FUEL MIXTURE ADJUSTMENT CHART
The following chart provides general guidelines on how
weather conditions and altitude affect air density when
they move higher or lower than your baseline setting.
IF IS Creates an air Required Tuning
density that is Adjustment
Temperature Higher Less Dense Leaner
Lower More Dense Richer
Humidity Higher Less Dense Leaner
Lower More Dense Richer
Pressure Higher More Dense Richer
Lower Less Dense Leaner
Altitude Higher Less Dense Leaner
Lower More Dense Richer
Nitro % Higher N/A Richer
Lower N/A Leaner
TUNING ENGINES BY TEMPERATURE
Do not rely on a temp gauge alone to tune your engine as
there is NO optimal temperature that will deliver the best
tune on any given day. Factors such as track conditions,
driving style, atmospheric conditions, and gauge accuracy
will affect operating temperatures
Tune the engine by paying very close attention to how
it responds to changes in fuel mixture (more smoke/
less smoke, fast/sluggish, reliable/stalling, smooth
sound/ muffled sound, etc). Remember to make small
adjustmentsof1houratatime.Imaginetheslotin
theneedleislikethehourhandonaclock.Adjustitas
though you were moving the hour hand from one hour
to the next or previous one. Once the engine is tuned for
acceptable performance, then observe the temperature.