I once considered investing in a ColorTune kit, but having
read the recent discussions I think I will stick to my
present method. Namely, comparing the discoloration of the
center insulator on each plug.
I have 3 SUs to tune on my E, hence my concern about getting it
right. The first time you have to set things up as close as you can
using the standard technique of monitoring rpm while you tweak.
Any manual will take you through the steps. I did find the air
balance to be critical though, and so I did buy one of those
little venturi flow meters. This showed me for example, that it
was vital for the throttle butterflys to close equally.
Next, you accumulate a few miles of fun driving, as fast as your
local police allow you. Then you take all the plugs out and lay
them on a sheet of paper in sequence. The colour of the plug
insulator tells all:.
Blackish - too rich; grey-white - too lean; chocolate brown - just
right. Having all the plugs side by side really helps to see subtle
differences. I have iterated this process a few times over a couple
of hundred miles and made the finest adjustments imaginable. All
6 plugs are now the color of the finest Swiss chocolate, or should
I say English toffee.
All this is too slow and tedious, I hear you say. Patience - if you
want a well tuned motor you have to come back to it a few times, and
we all love to tinker otherwise why did we buy such a car? The
main advantage in my mind is that you see the result of your tuning
averaged over the whole performance range that you have been driving
in. If you have been running to lean and risking burning your valves
you will see at once little droplets of molten plug on your insulator,
and the edges of the gap eroded away. Too rich and you see obvious
fouling.
If you want to go the step further why not consider what is often
done on aircraft engines. The exhaust gas temperature is monitored
on each cylinder as this is a direct measure of combustion conditions.
High temperature - lean; low temperature - rich. My friend's Mooney
has an LED display of each manifold temperature - my eye's are
glued to them whenever we fly over mountains. I am sure a do-it-
your-selfer could attach thermocouple wire to each exhaust header
and make a readout device on the dash. Haven't tried it my self,
I am content with my plug colour.
Reminds me of the anecdote of the Italien pit stop mechanics who
could spot a fouled plug mid race by spitting on each manifold in
turn, much as you would spit on a hot iron. My old professor
swears this to be a true story - anyone else heard it?
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