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All carburetors
are factory set on a flow bench. For this reason it is
recommended that you count the number of turns on the low and
high end needles before you use the engine. All carbs are not
the same, but are set to flow the same amount of air and fuel. Up to a one half turn difference can be had on
factory carburetor settings on each needle. A two
micron difference in the needle taper can make the setting up
to 1/2 turn different from another carb. It is also not
recommended not to adjust the mid-range
needle setting on your Picco, Sirio or Rossi until
you are completely comfortable with carburetor adjustment.
How big is a micron? There are 25,400
microns in one inch. This dot (.) is
approximately 1/64 of an inch wide and equals 615 microns. It
doesn't take much to off set a needle setting.
Picco
.12 - .15 (General Carburetor Settings: slide and
rotary)
New Carb -
4.5 turns out on the high
speed needle
2 turns out on the low speed needle.
(adjust while carb is wide open)
(see
picture "example 3" in side bar to determine your carb)
Old Carb -
2.5 turns out on the high speed
needle
2.25 turns out on the low speed needle
(adjust while carb is wide open)
(see pictures "example
3" in side bar to determine your carb)
Sirio
.12/15/18 (General Carburetor Settings)
High
Speed - 5.5 turns
Low Speed - 2-1/2 (Generally this should
be flush with the end of the slide)
Mid Range - Flush then
one turn out.
Sirio
.21 (General Carb Settings)
Low End: 2-1/2 turns
out
High End: 5-1/2 turns out
Midrange: Flush then ½
turn out
Rossi Black Magic (General Carb
Settings)
Low End: 4-3/4 turns out
High End:3 turns
out
Midrange: Flush with carb body
Novarossi NS12XX or RS12XXXX (General
Carb Settings)
Low Speed: 3.25 turns out
High Speed: 4
turns out
Mid-Range: Flush with the carb
body
Why is my new engine so tight at the top of
the stroke when I try to turn it over in my hand?
Nitro
engines are built with a taper in the sleeve to help seal the
piston and sleeve at the top of the stroke. When the engine is
new this can be very tight and the motor can get stuck on "top
dead center." Don't worry about this as the motor breaks in it
will "loosen" up a bit.
What is the "Top End"
needle?
The "Top End" needle is the large needle valve
that adjust how much fuel is delivered to the engine from half
throttle to full throttle.
What is the "Bottom End
or Low end" needle?
This needle adjusts how much fuel
the motor gets at idle and at the first crack of the throttle.
What does is mean when people say
my motor is "too rich?"
This means that there is too
much fuel being supplies and not all of it is being burned off
in the combustion cycle.
What does it mean when
people say my motor is "too lean?"
This means that the
motor is not getting enough fuel. This can make a motor
difficult to start or make it run too hot.
How do I
know if my motor is "too lean?"
A motor that is too
"lean" will not stay running. Usually will flame out at full
throttle or not idle. Temperature is one way to check this.
Another way is to examine the plug. The element in the plug
will turn close to "white" and be dry if the motor is too lean. This condition is very damaging to the motor since the
motor relies on fuel for it's oil supply as well.
How do I know if my motor is "too rich?"
A
motor that is too "rich" will spit raw fuel out of the exhaust
pipe and never really reach top RPM or "clear out" meaning to
not burn all the fuel. This motor will usually idle OK but
will bog and die the second the throttle is applied if the low
end is "rich" or never reach full RPM is the "top
end" is rich.
How do I read my plug?
(This section
courtesy of the late Ron Paris and Paris Racing)
OS and
Turbo glow plugs go gray sooner [easier] than McCoy plugs;
this is not necessarily bad. Actually when a new plug wire
just goes slightly gray after a 5 or 10 minute hard run it
means your very close to an optimal horsepower tune, but be
careful the next step is TOO LEAN!
Rule of thumb:
1} Wire and surrounding bottom of plug
wet, with
like new shiny wire = rich side of optimum power 85%
2}
Wire and surrounding bottom of plug starting to dry and wire
starting to gray = Very close to optimum power 95%
3} Wire
and surrounding bottom of plug dry, wire totally gray but not
distorted optimum power 100%
4} Wire and surrounding
bottom of plug dry, wire distorted = slightly lean DANGER!
5} Wire and surrounding bottom of plug dry, wire broken
and distorted or burnt up = extremely lean possible engine
damage!
Note: You can only "Read" your plug in a
nearly new state [Wire like new and shiny] A gray plug can
still operate well. But after it has totally gone gray
performance can start to fall off. To test just put in a new
plug and if there is no difference in performance save the
gray one or put it back in. If your engine does not feel or
run right tray a new plug before making major tune change's
How do I properly "break in" my new
motor?
Follow the manufacture's recommendations. This
is an important procedure, but the key is not to run the motor
too hot on the first few tanks and keep from using full
throttle.
What does it mean when people say I have
to adjust the "bottom end?"
This means you need to
adjust the low-speed setting on the carburetor.
How
do I adjust the idle?
The idle is adjusted by turning
the idle screw on the carburetor. This can be found by looking
at the manual that came with the motor. Turning the screw in
will increase the idle speed and turning the screw out will
decrease the idle speed. These screws are simply a stop for
the slide or barrel of the carburetor.
Why does my
car die after only idling for a few seconds?
This
usually means the low-speed needle (i.e. bottom end) is too
lean. Try turning the low speed needle out (counter clockwise)
about 1/8 of a turn at a time until the car will idle.
Why does my car die right after I accelerate from a
stop?
This again is usually a lean condition on the
"bottom end." Try "richening" up the low-speed needle by
turning it out 1/8 of a turn at a time until this condition
stops.
Why would I want a hot plug vs a cold
plug?
This is exactly how it sounds. If it is a very
cold day you should try a hotter plug and vice versa. This is
a trial and error process at best. Generally the .12's like
hotter plugs. You need to try both to see what works for your
conditions.
How far should I turn the needle valve
when I make adjustments.
Any needle valve should only
be adjusted in 1/8 turn increments. These are very sensitive
adjustments.
Are there "starting" points for my
needle valve settings?
Always follow the manufacture's
recommendations.
How do I know when my piston and
sleeve are too worn?
Usually a motor with a worn piston
and sleeve will be very hard to tune. Small adjustments will
make major differences in performance and overall power will
be much lower. You can feel when a motor has no "compression."
Compare your motor with another that you know is good and you
will notice that your motor will be very easy to turn over
with your fingers. It will not be harder to turn at the top of
the stroke.
How would I know if I have an air leak
in my carburetor?
This is a tough one. An air leak will
make the motor very very difficult to tune. Usually the idle
will be inconsistent and the motor will generally not want to
perform consistently. This is a difficult condition to
detect.
When I rev my car it seems to idle at a
higher RPM for a few seconds then settle down.
Why?
This could be from an small air leak in the carb,
or from a motor that is running a bit too lean.
Why
do people adjust the length of their tuned pipe and header
assembly?
Racers do this to adjust the power of the
motor. This is very noticeable on .21 motors and not as
critical on the .12 motors.
Rule of
thumb:
Longer manifold = more bottom end torque. [At
the expense of some rpm]
Shorter manifold = more top end
rpm [at the expense of some torque]
BUT you can go to far
with either direction causing the engine to run erratic or
HOT!
You must keep it in the "sweet spot"
Bottom line:
there is no set length for every engine or pipe, experiment
with the length to suit your driving style or track needs.
What does it mean when people say my clutch is "too
heavy?"
This means that the clutch is engaging too
soon. When the clutch engages too soon it bogs the motor,
which hurts acceleration. The motor needs to reach it's power
band at the same time the clutch fully engages. A good rule of
thumb for clutch adjustment is: if the car moves before you
see smoke from the exhaust, your clutch is engaging too
soon.
How do I "lighten up" my clutch?
If you
have a Centax style clutch you need to have it engage later.
Usually this is done by tightening the spring. On a shoe
clutch you can either run heavier springs or lighten up the
clutch shoes themselves so the it takes a more RPM for inertia
to engage the shoes with the clutch bell. Always take material
off the back of the shoes (i.e. the side that does not contact
the clutch bell.)
Does the clutch have any effect on
anything else besides acceleration?
A clutch that is
too "heavy" or too "light" can affect several things.
Obviously acceleration, if the clutch is too heavy a motor car
run hot and have lower gas mileage an bog on acceleration. A
clutch that is too "Light" will slip too much. This makes the
motor run at higher RPM's, kills acceleration and can also
yeild lower mileage.
What type of oil should I use
on my foam air filter?
We suggest any "tacky" petroleum
based oil. Motorcycle shops sell this for ATV's and dirt bikes
air cleaners. Don not use silicone based oils. K&N air
filter oil is specifically made for K&N filters and is not
good for use on foam filters.
Do
you have any "General" nitro motor break-in
guidlines?
- Open the high-speed needle one more
full turn from factory settings
- Open the low speed needle
½ turn more than factory settings
- Start engine and let
idle for 5 or 6 minutes
- Refill the tank and drive the
vehicle at no more than 1/2 throttle for the first three or
four tanks of fuel.
- Between every tank of fuel let the
engine cool until you can feel no heat in the head and make
sure the piston is at the bottom of the stroke during the
wait.
- On the fifth tank you can use up to full throttle
and after six tanks you can start to lean the motor
out.
- Rossi Engines may take up to a gallon of fuel
before fully seated. At about a half-gallon of fuel Rossi
Engines are about ready to race!
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