My '73 BGT with a mild fast road cam (real power rolls in >2.5krpm)
full 2" Peco free flow header, pipe and rear box. K&N free flows on.....
...well we'll start the story with the original HS4
AUD405's 1.5" carbs that were on the car when purchased.....
I went from stock AAE's to ABD's. Then to AAA's.
Pulling the choke at cruise (above 35 mph) seemed to make
the engine run much smoother with no change with all the
needle swapping. With many rebuilds, leak checks, poppet
valve soldering closed then new 'poppet-less' plates
Mileage was down in the 18-22 mpg range.
I bought NEW AUD405's. I figured HA! no air leaks. No more wondering.
WRONG! SAME PROBLEM.
I ended up swapping out biased needle pistons, (yes... out of brand
new carbs) for fixed needle pistons (used). I've been running #7 needles for
the last year (14K miles, daily driver) I average 24-28 mpg and the plugs
look good regardless of when I look at them.
IT STILL DOES IT! not NEARLY as bad, but still noticeable if you pay attention.
But the choke doesn't effect it anymore, other than during initial engine warm
up.
I've been able to prove to myself .... by reverting to a long ago lost
logistic....
driving by, and tuning the carbs and timing, with a vacuum gauge works great!
I've learned to tell quite a bit about the real 'run-ability of a particular
tuning state of the engine by watching what the vacuum gauge does
and how rapidly or steadily it changes or remains constant.
------------------- GUESS --- THEORY ---- BELIEF ---- WACKED OUT LOGIC----
this is a warning the previous line describes the following statement :-D
Air pulses/pressure pulses within the structure of
the intake ducting creates standing waves of pressure at their tuned
'resonance' as the valves open and close to the air flow.
I believe these standing wave are the culprit here. I do believe the
'pulsing' you feel in the drive train is actually acceleration pulses,
not drop-outs of engine horsepower.
Think carefully, when the pulse/surge/whatever-you-want-to-call-it,
transpires, you feel the light push from the seat, but it is sustained...
and then fades... you only notice it when it pulses again.
GUESS --- end of wack'ed'ness
------------------------------------------------------
If you are running lean, the engine will run much hotter at highway speeds.
If you come of the interstate 60-75mph. then hit a back road highway,
say 45-50 and the engine cools more than 2-3 gauge needle widths....
odds are your running lean, (or your timing is delayed.)
THE FINAL SOLUTION THAT SOLVED ALL THE PROBLEMS
The two little distributor springs that hold the advance weights.
They are designed to have just a weeee little bit of freeplay in the loop
that hold them to the posts. I've been able to measure (and prove to myself)
that the timing can jump around about 1-3 degrees do to this 'slop'
I proved to myself... (all I care about proving) by removing the weights
and only running vac advance. The difference was instantly noticeable,
and very predictable.
YMMV PAYOR
Paul Tegler wizardz@toad.net http://www.teglerizer.com
----- Original Message -----
From: "T. .R. Dafforn" <td214@cam.ac.uk>
To: "spitfires" <spitfires@autox.team.net>
Sent: Thursday, September 28, 2000 11:41 AM
Subject: needles
C'mon guys (and Gals),
Its unlike you guys to be quiet about getting extra performance out of
your spit...
Has anyone got ANY experience with richer needles in HS4 SU's and high
flow air filters?
And could I diagnose a lean mixture at high revs by pulling the choke at
high revs?
Cheers
Tim
--
Tim Dafforn
Structural Medicine
Department of Haematology
CIMR
University of Cambridge
Wellcome-MRC Building (Level6)
Hills Road
Cambridge
CB2 2XY
Tel. (01223) 336829
Fax. (01223) 336827
http://smokeroom.cimr.cam.ac.uk/
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