Alfetta timing: some success (long)

[drubie@xxxxxxxxxxxxxxxx (David Rubie)]

Executive Summary:  How to fix a stumbling Alfetta.

1) Reset the camshafts to the correct time.
2) Ensure the distributor advance is working, then
   set it to advance 37 degrees at maximum, don't
   worry about static advance or idle.
3) Balance the carbs.
4) Fix your Alternator !!!!!

I posted a query a couple of weeks ago about the correct
ignition timing on an alfetta GTV that was stumbling
at lower RPM's and received some very helpful replies
from the following people:

fayth@domain.elided (Obadiah Fayth) suggested I re-check the
cam timing, that his experience suggested "euro" cams
(which is what I have) should perhaps be set to 99.5
degrees, and other cams to 102 degrees.

Tom Sahines (tsahines@domain.elided) re-itereated the 102 degree sentiment on
the camshafts which I decided to follow.  I was extremely
careful when re-assembling this engine as I didn't want
the valves to touch the pistons.  As it turned out, the
cam timing marks on the camshaft caps were at 102 degrees
and I had my cams lined up exactly with TDC on the engine.
So the problem wasn't there.

Tom also suggested I pay more attention to the maximum advance
on the timing rather than idle.  He said his dyno work had
identified 37 degrees maximum advance is probably enough to
work well without pinging on US premium fuel.  Down here in
OZ we use some sort of different octane measurement, but his
suggestion seemed to work great.  What worked even better
was throwing away the stripped bolt on my distributor that
allows the thing to gradually lose adjustment, which turned
out to be about 10 percent of my overall problem.

Andrew C sent some excellent instructions on how to modify
the advance curve on a Bosch distributor which are a great
supplement to the kartalamakis performance tuning book.
I finally realised why this book's instructions confused me.
My Bosch distributor isn't the same as the one in the book.
Instead of having a "primary" and "secondary" spring setup
which allows two different parts to the curve, the Aussie
distributor seems to have two springs which work in concert
with each other.  No matter.  I can forward Andrew's description
to anybody who wants it.

Damian Carvolth suggested an alternative method for determining
the maximum ignition timing which I'll include here:

damian@domain.elided wrote:
>The ideal solution is to put it on a dyno, but given you won't want to spend
>$100 or so on that then the next best thing is to get a vacuum gauge hook it
>into the intake manifold (any port will do provided your carbs are balanced)
>and advance the distributor until the vacuum peaks then back it off about
>1/2" - 1" mercury. That will give you optimum advance at those revvs with an
>allowance for load to prevent pinging. Having done that mark the position of
>the dizzy and do the same thing while revving the car (this is why a dyno is
>ideal) noting whether the dizzy is at the same place for peak vacuum at
>higher revvs. It should be unless alfa did something weird.

I didn't try it, but it did inspire me to buy a "Carbalancer" to
check the balance of the carbs.  They were out by a bunch.  Tuning
by ear is no good if you don't know what to listen for :-)  That 
Carbalancer looks cheesy, but it works.

All this had my head scratching.  The car was better but not brilliant.
Then, driving home the other night, the voltage idiot light starting glowing
slightly, then got brighter and brighter as the headlights got dimmer
and dimmer.  The car *really* started stumbling, further into the rev
range.  When the cooling fan kicked in, the whole car nearly died.

I coaxed it home (the last 1/2 kilometre without headlights) and
contemplated setting it on fire.  Then I parked it for a couple of
days and drove the Mazda to work.  Obviously the alternator was dying
but why?  The extra stumbling as the battery flattened gave me a clue
that the problem I was chasing was electrical in nature anyway.  The
Crane XR700 ignition I am using is *very* sensitive to having a good
earth, so there's no reason why it wouldn't be affected by low voltage.

I pulled the alternator this weekend, but needlessly.  As I was pulling
the power wire nut off, the wire itself popped free of the crimp
connector, showing a green, corroded end.  I replaced the wire with a brand
new one (threw in a new solid state regulator too).  I did pull the
alternator to check the bearings and brushes but they were fine.

Once reassembled, the car now runs pretty well.  There is the odd stumble
(which I think is to do with the progression of the 45mm carbs) but
it now pulls from 2000-6000 without a problem and the mid-range is
especially impressive.  I don't know how long the car has been coping
with a low voltage output from the alternator, but all the lights
are much brighter...

Thanks again to everybody who replied.

dave.

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