| The hardest part of 1/8 scale racing
is fine-tuning the engine. You need to learn this on
your own. Spend some time, even an entire practice day,
developing this skill. Always remember, it never hurts
to have the fuel mixture too rich, but never, NEVER
let the mixture get too lean.
Basic
tuning procedure is as follows:
1 - set the engine’s idle speed
up slightly higher than normal
2 - start tuning your engine with
the settings too rich
3 - always tune top end first
4 - tune bottom end next
5 - reset idle speed
You tune the engine by measuring the
engine’s temperature, and making the required adjustments
to make the temperature correct. There are two ways
to measure the engine’s temperature:
a) Temperature gauge method: Get the
engine up to running temperature, bring the car into
the pits and immediately take a temperature reading.
Place the temperature gauge directly over the engine,
pointed at the glow plug, and take a reading. It’s
easier to do if you have a second person to take the
readings for you.
b) Spit method: Get the engine up
to running temperature, then pull in as quickly as
possible and put some spit on the engine’s cylinder
head (quickly, so as to not burn your finger). The
saliva should just slowly boil off (2 to 3 seconds).
It should NOT dance around as if it were on a hot
griddle, nor should it lay there and steam. In short,
if your spittle will sizzle, it's too hot.
If the engine is too rich, the engine
temperature will be colder than desired (and vice
versa). If the engine is too lean, the engine temperature
will be hotter than desired. Go out on the track with
the top end rich. If you have got the mixture set
right, there will be heavy smoke from the engine on
the straightaway. Run four or five full laps to get
the engine up to running temperature before touching
the carb. Bring the car in, and take a temperature
reading. Start leaning out the top end by turning
the adjusting screw only 1/12 turn at a time (picture
a clock’s 12 even spaces). Take your time doing the
adjusting - don’t be in a hurry. It may take a while.
Your goal will be to get the car to just "punch
clean" when you come onto the straightaway, which
is what it will do when the mixture is set properly.
For 1/8 scale cars, you will have the correct mixture
when the temperature is about 200 degrees. The 1/10
scale cars run a little hotter, maybe around 250 degrees.
Once you think you have the top end
set, run 3 or 4 laps, then stop the car close to you
on the track and let it idle for 5 seconds, then "push
off". It should have slightly loaded up, but
still accelerate quickly. If the engine died before
the 5 seconds, check the following:
If the engine seemed to load up and
slowly stop, it was probably too rich.
If the engine’s idle speed increased
before it stopped, it was probably too lean.
Always run a few laps before testing
bottom end and idle. Ron likes his car to idle clean
for 5 seconds, but by 6 or 7 seconds his engine loads
up when he punches off (heavy smoke with a slight
stumble). At this point you may have to re-adjust
the engine’s idle speed. If the idle speed is too
high, the clutch will not release completely and you
will lose "snap" off the corners. If the
idle speed is too low, the engine may stall on the
starting line, or at the end of the straightaway when
you let off the throttle.
Things to Remember:
1 - Never try to tune a cold engine!
2 - Adjust top end first
3 - Always tune from rich to lean.
If in doubt, richen it up first.
Your glow plug wire should stay bright
like chrome. If it turns dull, or gray, the engine
was probably too lean on top or bottom, or both. Note:
wire may also distort or be burned up if it’s too
lean. If glow wire is still shiny like new, but distorted,
you may have to add a 0.004" shim or use a lower
percentage of nitro.
Over 99% of all engine complaints
are usually related to the tuning of the engine or
clutch. |
