Considering that there is, theoretically, one perfect setting for tuning a
car, their are more opinions available on how to do it than you can shake a
stick at. Reading the plugs at full throttle, high RPM is the safest
approach since that is where you are most likely to damage the engine by
letting it go lean. However, manufacturers, having some sense, usually
design the fuel curve such that this operating range runs on the rich side
when the cruise mixture is correct.
SU's are wonderful devices but they are not the world's best fuel mixers.
One of the reasons that our LBC's run such terrible mileage is that they do
not lean out enough at cruise. They respond to the velocity of the air
across the jet bridge such that a given velocity of air gets a given amount
of fuel. This in not what you really want. An engine accelerating at low
RPM and an engine cruising at high rpm may have the same air velocity but
they would optimally use very different mixtures. On Acceleration, you
want to be around 110 to 130 percent fuel which is the "best power" range
if I remember correctly. At cruise, you would want to lean down below 100
percent to the "best economy" fuel air ratio. Engine tolerate rich
mixtures better than lean mixtures so you tend to tune on the rich side in
general so that you never fall below the lean limit.
Personally, I tune my carburators the same way that I set my timing- by ear
and experimentation. I first use standard tuning to get the carbs tuned
equally. I will then adjust them both richer or leaner until I am
satisfied with the way the car runs. This usually involve leaning it until
I start getting flat spots or until I feel that I have to use the choke too
much then going back rich a flat or two. I watch the plugs during this
process to make sure that I am not doing anything stupid. Some people
claim that you can read the exhaust pipe, too but I have never developed
that skill. The best gage is exhaust temp, in my opinion but very few of
us have pyrometers in our cars.
On the subject of pink cars, I was driving my Spit**re a few years back
and passed this Pors**e 914 that was painted "Mary K Pink." I waved to the
driver but he looked embarrased to be seen in the car. Maybe his wife won
it but there is one case where I would spring for a paint job even though
it isn't needed.
Over the weekend I discussed naming the A with my family. As of now the
top candidates are:
Abby- in honor of Abingdon
Miss Gwenn- the correct initials and a nod to King Arthur's SO
Anyway, I am still working on it.
This weekend my SO and I went for a ride. This is significant since she
considers my cars to be more trouble than they are worth. In the 15 years
that we have been together, she has ridden in one of "my" cars less then
ten time total. She never rode in the Corv**te (an interesting story) and
took three years to do two rides in the Spitf**e. She has already ridden
in the A twice now and I believe she enjoyed it! Further proof that MG's
have a magic of their own.
Regards,
Bill Eastman
61 MGA
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