Jim Cawrse wrote:
> For all:
> Sunday afternoons I have taken to hanging out with a guy in the
> neighborhood who has several MGs. He bought a color tune and
> wanted to know how it worked (great guy, not very mechanically
> inclined). Well, we tried it out on the Datsun. Its basically a
> generic spark plug with a glass window. When you start the
> car you can see the color of the flame taking place in
> the combustion chamber. I did the forward cylinder and the
> aft cylinder. Both burned with a Bunsen burner blue flame
> which is supposed to be exactly right. Interesting that when
> you blip the engine, you get a moment of yellow flame, indicating
> a rich mixture on acceleration, just what a well adjusted SU
> is supposed to do. When you suddenly close the throttle you
> get some yellow flame for a second or so also. This would seem
> to me to be the hydrocarbon rich air polluting phase that the
> air pump was supposed to help do away with on the 68-70 cars.
>
> Bottom line, if your car is running great, no need for this thing,
> but if you can borrow one while tuning carbs, it could be
> a useful tool. BTW, my spark plugs are a very dark tan,
> indicating a mixture just on the rich side of exactly right,
> which agrees closely with the color tune.
Two words of warning on these.
1)if you do not put your engine under load when using these, the mixture
settings will be wrong. May not make much difference at idle, but at
WOT, it can mean the difference between a hole in your piston or not.
2)unless your engine is absolutely bone 100% stock, setting the idle
mixture with this or any other tool on an SU will not work well. Unlike
almost all other carbs, the idle setting also affects all other phases
of operation on an SU, and the most critical is WOT at redline. On a
modified SU powered engine, you need to set that correctly and live with
the mixture being wrong everywhere else (unless doing that creates a
serious leanout at part throttle cruise, in which case you need to reach
a compromise between proper mix there and proper mix at WOT redline).
Again, all of this must be done with the engine under load, which means
a chassis dyno.
--
Marc Sayer
Journalist, Photographer, Dog Trainer (APDT member #062956)
Passions -
Great Danes, auto racing and fast cars, my wife
Dogs -
Gracie, Tank, Delilah, PJ, & the rescue dogs
Cars -
82 280ZX Turbo, 83 Volvo 245, 93 Ford E150 Tow/dog van
71 510 Trans Am vintage racer, homebuilt Formula V
My Homepage - http://gracieland.org
Deaf Dane Rescue Homepge - http://gracieland.org/DaneRescue/
Any Dane at the races is a Great Dane!
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