I have a ColorTune that I used on my Mini and thought it was great for all
around tuning until I was set straight by my mechanic friend the "Miniman".
(BTW Miniman is a British car garage in Ottawa,Ont Canada that does mail order
as well, and you guessed it, are Mini experts(among other things)....plug over!)
There is no question that it works great for doing mixture adjustments as well
as troubleshouting. The important point in all of this is that it does the
analysis under NO LOAD conditions. Yes you can rev the engine up to red line
with the ColourTune in place but the requirements of a reving engine with 0 load
has no relationship whatsoever with an engine under load. If you are only
worried about setting up the idle mixture of a non-modified stock engine then
this is the tool for you.
If you have modified your engine and are attempting to determine whether you
have the correct needle profile in your SU this tool will do nothing for you
except allow you to set the idle mixture.
I have since invested in an air/fuel ratio monitor from K&N filters. It was
very expensive(can you say....rip-off!!) about $150 or so. It is basically a
standard production oxygen sensor that all modern cars use, coupled with a
very basic LED bargraph display about 2" square. I'm sure the display unit has
about $10 in parts in it (if that) and the sensors can be bought for around $50.
Check out J.C. Whitney, they have one for much cheaper.
You have to weld in a fitting into the collector section of your header since
the sensor must be at a minimum temperature to operate properly. After that
you can simply read the bar-graph which tells you whether the air/fuel mixture
is rich or lean. A correct air/fuel mixture value is a standard thing and does
not vary for different cars. The output of all sensors (whether american or
japanese or other import) is the same so you can simply go and get ANY one off
of a used car at a wrecker(if it isn't rusted in). The thing you are paying for
is a CALIBRATED display unit.
This is the exact same set-up that is used on many dynos to set up the mixture
on engines being evaluated. The most important point about all of this is you
are visually checking the mixture UNDER LOAD CONDITIONS while the car is in fact
in a real life situations.
My only problem is knowing how to interpret what point on the needle profile
has to be shrunk or enlarged to tune the mixture for particular revs. On a
dyno you can simply look down throat of the venturi on an SU and see how far up
the needle has risen out of the jet. If the mixture was lean then you file the
needle at the appropriate point. If it is rich, then you swap in a needle that
is thicker at this point. I've been tempted to cut a hole in my dash and run
the SU without a filter so I can get my passenger to look at the needle
position for various revs/gears through the hole and down the venturi!
But you are fooling yourself if you think that your mixture on your modified
engine(any modifications!) is correct if it has been set at idle only and under
no load conditions.
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