This is a hard one to explain simply (briefly) but here goes.
Apparently not all the lists got the info about the real cause
of the problem. Although this was on an '73 MGBGT, my '75 Spit was
exhibiting (although just slightly) some of the same symptoms.
It turned out to be a combination of which vac. advance curve,
(where it starts, ends, and total advance supplied) which
source of vac is being used, (ported or manifold)
and the mechanical advance curves and engine/dist
mech. timing.
If you look at my advance curve charts for Lucas dizzies
( www.teglerizer.com/mgstuff/advance_curves.htm )
which by the way was compiled while trying to sort all this out
and was also why Paul hunt (MG list) started putting one together
after mine was started)
look carefully at the curves and where vac advance starts
and ends vs whether it's ported (carb connection) or
direct manifold connection.
NOW HERE'S THE KEY TO IT ALL.....
think through throttle position and what effect the curve
and amount of vac avail would have for various throttle
positions and how much advance would be added/subtracted
from the total advance avail for that throttle condition.
I had tried various distributors, and vac units, ...rebuilt
and buggered up on purpose.... both manifold and ported
configs were tested.... still stumbled at cruise.
New carbs were purchased still nothing helped.
I finally went back to a previously tried configurations,
then purposely rearranged vac source to what.....
SHOULD NOT have been correct for that model year.
...sure enough, configured as an earlier year everything
was resolved.
So it turned out my engine was running an earlier model year
cam, so the dist, (mech. adv.) and vac pot., vac source, were the wrong
config. I changed the dist back to the previously tried config
but changed the vac source to port correctly match that dist.
All is well.
So on my '73 GT, I'm now running 1970 spec dist, vac pot.
cam and ported vac advance.
On my 1975 Spit, I have removed the elec distributor
(box on the side) with vacuum retard vac. pot. that already had
a Pertronix Ignitor in it and replaced it with and earlier model
(different curve). I changed out the advance curve plate
(swapped out the 6 degree plate for a 10 degree plate)
and went to ported vac. Careful engine timing (dist vs crank)
is now crucial, as the dist. vac advance lost under heavy throttle
has to be balance with mech. advance and idle.
I'm going to still have to play with the Spit a bit
to resolve the tendency of the car to pick power just slightly
as I back off to shift gears. (vac advance comes in
just as I let off to shift giving a seemingly surge of power
after hard acceleration)
I told everyone I would write this all up, but the project has gotten
out of hand. After nearly 2 years of analysis, troubleshooting
and list questions (nearly 400 emails on this subject...both Q's + A's)
It reads more like a book on advance curve requirements,
control, and design.
If I can simplify all the tech info down to common user language
it may just still get posted yet. :-)
Paul Tegler ptegler@gouldfo.com www.teglerizer.com
----- Original Message -----
From: "Jeff McNeal" <jmcneal@ohms.com>
To: "Ptegler" <ptegler@gouldfo.com>; <spitfires@autox.team.net>
Sent: Monday, February 26, 2001 10:05 AM
Subject: Re: Ashamed of the 'tools' was 1500 tools
Hey Paul,
Did you ever post details on whatever whiz-bang solution you came up with
for your poorly idling Spitfire based on a question from a six-year-old lad
who was watching you work? Posting the tease for your amazing revelation
without follow-through is more shameful IMHO than discussion about
assembling a toolkit for cars, some close to four decades old, that owners
don't want to risk leaving along the side of the road if a component fails
some time while driving!
Best wishes,
Jeff in San Diego
'67 RHD Spitfire Mk3 aka "Mrs. Jones"
'68 LHD Spitfire Mk3 frame-off resto project
Jeff's Classic '67 Spitfire Mk3 site & Vintage Spitfire Webring
http://www.ohms.com/spitfire/spitfire.shtml
home of the NEW Totally Triumph Auction
"By Triumph enthusiasts, for Triumph enthusiasts"
http://www.ohms.com/cgi-bin/TRauction.cgi
and..The Totally Triumph Garage forums -- moderated, focused, friendly!
http://www.ohms.com/cgi-bin/dcforum/dcboard.cgi
...plus a few other surprises!
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
----- Original Message -----
From: "Ptegler" <ptegler@gouldfo.com>
To: <spitfires@autox.team.net>
Sent: Monday, February 26, 2001 7:16 AM
Subject: Ashamed of the 'tools' was 1500 tools
>
> Quite frankly... I'm a bit ashamed of all this tool talk.
>
> My x2b drove the her '77 Spit (original owner back in '77)
> for 14 years and 142K miles as a year round daily driver.
> We never carried tools...and it never left us on the side of the
> road. EVER!
> So too was the story of my 1980. The only time I didn't get
> home from a trip (in the '80 back in '82), was when I rolled it to avoid
> a 'head on' with an old farm truck barreling around a corner
> over the line.
>
> These days I've yet to carry any tools at all... other than
> extra coolant, oil, a can of fix-a-flat (I don't bother carrying a jack)
> and a flat tip screw driver to play with the carbs occasionally.
>
> So... I guess that makes me a fool?
> ...or do I simply trust my babies, knowing they're paying me
> back for the quality of attention they receive? :-)
>
> Paul Tegler ptegler@gouldfo.com www.teglerizer.com
>
>
>
> ----- Original Message -----
> From: "d t gebhard" <kimkell@decaturnet.com>
> To: "Michael Hargreave Mawson" <OC@46thFoot.com>;
<spitfires@autox.team.net>
> Sent: Monday, February 26, 2001 9:09 AM
> Subject: Re: Spitfire 1500 tools
>
>
>
> This should be the LAST word on this
> subject....Does anyone think that maybe we could
> carry a *spare Spitfire* in the boot,just in case
> the original breaks down!!!!!!!
> Dave Gebhard
>
>
>
>
> ----- Original Message -----
> From: Michael Hargreave Mawson <OC@46thFoot.com>
> To: <spitfires@autox.team.net>
> Sent: Monday, February 26, 2001 2:22 AM
> Subject: Re: Spitfire 1500 tools
>
>
>
> In article
> <3.0.1.32.20010225143600.008797e0@pop.xs4all.nl>,
> Eric
> Kieboom <ekieboom@xs4all.nl> writes
> >
> >At 08:54 25-2-2001 +0000, Michael Hargreave Mawson
> wrote:
> >
> >>The rest of the kit that's in there
> >>at the moment is as follows:
> >>[...]
> >>Restoration Guide
> >>[...]
> >>pair of carburettor rebuild kits
> >
> >And you had something to say about me carrying a
> set of feeler gauges?
>
> Though it be madness, yet there's method in't! (I
> bet I've misquoted
> that.)
>
> The restoration guide is in the boot simply to have
> it to hand when I'm
> working on her. All those pictures can be very
> handy. The carb
> rebuild kits are there because I haven't got around
> to doing them yet -
> and they *desperately* need doing. My idle speed
> at the moment ranges
> from 1800 rpm to a dead stall. With the
> accelerator flat to the floor,
> she bounces like a kangaroo with dysentery,
> although she goes like a
> rocket with slightly-less-aggressive acceleration.
> >
> >If you think it's necessary to carry around a
> restoration guide and carb
> >rebuild kits, perhaps you should also stuff a
> spare head gasket in the
> >boot. A friend of mine actually did a roadside
> head gasket change on his
> >Mk3 while on holiday in England. He's very proud
> of that stunt and brings
> >it up whenever he can.
>
> I'm not surprised he's proud of it. How on earth
> did he manage to skim
> the head before reassembly? A Universal Mill
> attached to the cigar
> lighter? <g>
>
> ATB
> Mike
> --
> Michael Hargreave Mawson, author of "Eyewitness in
> the Crimea,"
> to be published by Greenhill Books on 28th March,
> 2001:
> http://www.greenhillbooks.com/booksheets/eyewitness
> _in_the_crimea.html
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