Low-Speed Setright Needle Valves; Why Would Fuel Go "Bad - Horizon Hobby .40NX Evolution User Manual

2. Close the throttle slowly. You will adjust the
low-speed needle setting by rotating the
SetRight adjustment bar clockwise to lean
the engine and counterclockwise to richen the
engine.
CAUTION: Do not attempt to adjust the low-
speed needle valve while the engine is running.
3. The fuel mixture should be adjusted as
follows: The low-speed fuel mixture is too rich
if, when opening the throttle moderately quickly,
the engine emits smoke and "stutters" or
"stumbles." Correct this by rotating the SetRight
adjustment bar clockwise in small increments.
Continue this process until the engine transitions
smoothly from low rpm idle to high rpm without
hesitation upon opening the throttle
moderately quickly.
Step 2. Low-Speed Needle Adjustment, cont.
4. The low-speed fuel mixture may be too lean if the
engine stops at the lowest idle position or it stops
when the throttle is opened moderately quickly
from the idle position. Correct this by rotating the
SetRight adjustment bar counterclockwise in small
increments until the engine transitions smoothly
without hesitation upon opening the throttle rapidly
from idle.

Low-Speed SetRight Needle Valves

The design of the SetRight needle valve system is such
that, during normal operating conditions, the typical
user will find that the range of adjustment allowed by
the system is more than adequate for most situations.
As a matter of fact, we intended this to be used as a
tool to identify operating problems. If you find that the
range of adjustment allowed by the SetRight needle is
inadequate after your initial period of running, then a
problem in your engine system has occurred. This might
be a bad glow plug, dirty or old fuel, an air leak in the
fuel system somewhere or any number of other reasons.
Do not make any permanent adjustment range changes
to the SetRight needle system if it was once working
correctly for you and now does not. Investigate other
problems first.
However, occasionally due to atmospheric, altitudinal
or fuel conditions, you may find that the range of
adjustment built into the SetRight needle valve system
is inadequate for your needs. These conditions are rare
and easy to fix.
Low-Speed SetRight Needle Valve Correction
Should the low-speed SetRight needle valve
need to be adjusted outside the factory-
established parameters, follow these steps:
A. Loosen the setscrew found on the ring of
the SetRight assembly to which the
adjustment bar is attached.
B. Rotate the needle valve itself (small
slot-headed screw inside the blue ring of
the SetRight assembly) clockwise to lean
the mixture or counterclockwise to richen
the mixture as desired.
C. Retighten the setscrew on the ring of
the SetRight assembly and you have
re-established a new range of motion.

Why would fuel go "bad"?

The largest portion of the fuel is methanol (alcohol).
Methanol is hygroscopic; it attracts moisture. This can
cause your fuel to be contaminated with water, which will
cause poor engine performance. Additionally, the UV rays
in sunlight will eventually break down the nitromethane if
the fuel jug is stored in sunlight for long periods of time.
How can you tell when your fuel has gone "bad"?
The first indication will generally be the inability to start
the engine at previously run needle-valve settings.
Another clue might be that the engine has very poor idle,
runs but bogs down tremendously during run up and/or
will not attain the same rpms that you are used to.
How do I keep my fuel fresh?
If you have the opportunity, look for someone at a flying
field on a sunny day who has a jug of fuel that is only
1/4 full. What you may notice is that there are droplets
attached to the top and sides of the container. This is
the moisture in the air that is condensing inside the jug
because of the greenhouse effect of the semi-translucent
plastic jug. This will also occur within a metal fuel can as
the sun warms the contents.
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