original position then you are running
rich. This indicates that engine is not
completely burning the slug and that
residual fuel is being left in the cylinder.
You can start by leaning in the engine
and possibly looking at using a colder
plug. The thicker coil in a colder plug
will retain the heat better for the next
burn.
7. The coil is distorted and or dusty
white, broken or missing and the body of
the plug may be discolored and the plug
is completely dry. This would indicate a
dangerously lean condition for the
engine. You may also see signs of pitting
on the face of the plug indicating pre-
detonation. Running your engine like this
for any length of time will also pit your
piston and head button. It’s always a
good idea to pull your head button from
time to time and inspect it for pitting.
Running an engine too lean will also
deprive it of the necessary lubrication to
keep the internal moving components of
the engine well lubricated.
I hope you have found this
information helpful. I would love to hear
from anyone who has different ideas or
can expand my knowledge in this area.
Please contact me at
daves@concentricsinc.com
News from District 19
By Ted McKay
District 19 Director
Hello everyone. I thought I would
give you a short review of what's been
going on in District 19 the first half of the
year, and it has been quite a bit!
With the addition of the new Zenoah 28.5
we now have a NAMBA legal G-2
motor. At first, this caused a concern in
our district as we have the problem of too
many entries at our District races. We run
as many as 50 to 60 heats a day and
sometimes more. Understand this is a
nice problem to have, but there was a
concern by some members that we would
not have enough time to run all of our
classes each day. As it turned out, the
entries in G-2 did not happen however
we have had some heats of GX-2. I was
also concerned that racers might
mistakenly use these motors in G-1 and
GX-1.
Continued on page 18
PROPWASH
November 2012
17
Reading the Plug
Reading your plug is probably one of
the most important skills you can learn
to become a more competitive racer. The
glow plug speaks volumes about how
your engine is tuned and running, and
with some tips and some practice you
can build a solid understanding of how
to tune your engine just from reading
your plug. First of all, I always pull my
plugs after a race and inspect them. This
serves two purposes: first, if the plug is
damaged or is about to fail, I can catch it
and replace it before the next heat, and
second, to read the plug to tell me what I
need to do in the next heat to further tune
the boat. When we have pulled the plug,
here is what we might see:
1. The coil is shiny, the body of the plug
is not discolored and is dry and the face
of the plug is shiny or has a slight brown
color. This is a perfectly burning
plug. Because the plug is dry we are
burning all of the available fuel. The coil
is shiny or dusty and is not distorted so it
is running in a heat range that is good for
the plug and good for the engine.
2. The coil is dusty white, the body of
the plug is not discolored and is dry and
the face of the plug is shiny or has a
slight brown color. This is an engine that
is running slightly lean but very near
optimal performance. By richening up
the mixture slightly you can achieve
optimal performance.
3. The coil is shiny and the body of the
plug is not discolored but the plug is a
little wet. This is a plug and engine very
near optimal performance. You are
running slightly rich at a good engine
temperature. To achieve optimal
performance you may need to lean the
engine very slightly.
4. The coil is compressed or pushed
inside the body of the plug and may be
slightly distorted. This is an indicator
that you may have a timing problem and
you may need to advance the ignition
timing by using a hotter plug and
lengthening your pipe.
5. The coil is missing usually indicates
that your timing may be too early,
meaning that you would have to use a
colder plug and shorten your pipe. At
this point you may be suffering from
pre-detonation.
6. If the body of the plug is wet and the
coil is shiny and completely in its
Why then would we want to select a
“colder plug” if we have more difficulty
igniting the fuel? The reason we use a
colder plug with more nitro is to allow
the slug to be compressed more, thereby
increasing both the density of the
methanol molecules and also increasing
the temperature and volatility of the
nitro in the plug.
Generally speaking, a hotter plug
will give you slightly higher RPM and
will have better idle and transitional
characteristics. If the plug is too hot
your engine can suffer from pre-
detonation and you will lose power,
RPM and it can damage your engine. A
cold plug will give you better power
characteristics throughout the mid-range
at the expense of smooth idling and
some top RPMs.
I am sure all of you have experienced
the situation where an engine dies when
you pull the starting battery off: as long
as we have the battery attached, the
engine runs, but as soon as we pull it off
again it dies. This is a simple problem to
solve and it once again illustrates the
difference in plug temperatures. Simply
put, the problem is that the coil is not
hot enough to continue the catalytic
process after you remove the battery.
The tricky part here is that it could be
caused by a number of things each
demonstrating something about the
plug. First is the possibility that the coil
on the plug is damaged and can no
longer retain enough heat to burn the
next time, and in this case we simply
replace the plug. The second cause
could also be an idle mixture that is too
rich. As too much fuel enters the
cylinder it quenches the plug, in which
case we would need to lean the idle
mixture a little; because the hotter plug
has a smaller, thinner coil, it is more
easily quenched. It could also be caused
by a very high nitro fuel where there are
not enough methanol vapors to
effectively cause the combustion, and
finally we could be running too cold a
plug that is never getting hot enough at
idle to keep the catalytic process going.
We could also have any number of these
issues working together, so you can also
see how a very simple symptom can
yield a lot of information about what is
going on with your engine.