Thanks for all the input so far.
I already have very thin oil in the dashpots.
Please correct me if I'm wrong here. But as I see it is; as the needle is
drawn up through
the jet it tapers. If the mixture was lean I would want the air valves to rise
faster to supply
more fuel to the mix. If it tapers too quickly you get too much fuel.
The B1AF is designed for 2 carbs on six cylinders and I believe has a fairly
quick taper
as each carb had to supply three hungry cylinders. With three carbs each carb
is doing 2/
3's of the work it was meant for. If there is a needle with a more linear
taper it should
smooth out the mixture.
Altitude is easy to dismiss until you experience it. Anbody that lives below
4,000 feet
should hop on a plane to Denver and sprint down the Terminal at Denver
International
Airport if you don't believe me. The air really is thinner up here so a
needle profile that
works for sea level will most likely be rich at this altitude.
TR3's and I believe early 4's had three needle options for the carbs, a lean,
normal and
rich the TR6 has but one. The Haynes ZS manual has a listing of widths
measured every
1/8 inch for all of their needles. There is even a table that lists all of the
Biased needles
like the B1AF. These needles should fit directly into the 175CD's. If one of
these doesn't
work then I could move on to the greater selection of SU's. I just don't have
an
appropriate program to model the profiles of the needles (I have to talk to my
engineering
friends).
To sum up. The drop in power is from too much fuel, if the needle tapers too
quickly then
there is too much fuel (at least that is my thought). There is already very
thin oil in the
dashpots. I know my advance curve is not as agressive as it needs to be.
Thanks for the
offer RML but I am already taking steps to remedy the advance curve.
The other unmentioned factor is that the Dyno time costs $80/hour or $65/ for
three pulls.
Of course the $80 is the better deal because you can get more than three pulls
in unless
your doing major surgery. So even with suggestions it will be a while before
I can test
them.
So please, If I am way off on my thinking about the needle profiles please
let me know.
Shawn
>===== Original Message From tr6taylor@webtv.net (Sally or Dick Taylor) =====
>Shawn---I started to write a long reply to your post, regarding the fuel
>monitor picking up the bump in richness at 3,000. It got so unweildy I
>quit writing. There's too much for me to say for this type of forum, so
>I'll just hi-lite a couple of things.
>
>Yes, you can find out exactly what part of your needles is responsible
>for this increase in richness. You'll need to see where the air valve(s)
>are, in relation to leaving the bridge. This area of the needle will
>have to be wider. There are temporary ways of "thickening" the needle,
>one identified. From there, you can do to the SU chart to see if a
>commercial is available.
>
>First, I would "paint up" the needles now being used, to see if these
>mods make the monitor show the results you desire. It's very tricky,
>because you have to do the same thickening on all three of your needles.
>(Unless you have isolated each carb with its own 02 sensor)
>
>For a really good book on this, pick up a copy written by Des Hammill,
>on "How to Power Tune the SU Carburetor". (The same principles apply to
>the ZS carb).
>
>More on this, if you wish...
>
>Dick
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