105 Cams and ignition timing on Alfetta

[drubie@xxxxxxxxxxxxxxxx]

I am currently attempting to tune my '78 Australian
Alfetta GTV without a lot of success except when
I do things that aren't in the owners manual.

Basically, the problem is this.  I have replaced
the original cams in my 2 litre with a set from
an earlier "105".  The purpose, of course, is to
extract a little more power from it, as the cams
supplied with the car were a little more restrictive.

The problem seems to be that the factory ignition
timing marks do not work with the cams.  There
doesn't seem to be enough advance, especially at
low RPM's, causing the car to judder under load
and low revs (not detonation, just missing).

I have experimented with advancing the timing
by a few degrees and it seems to alleviate the problem,
but I was starting to worry that while the low part of
the curve would be adequately compensated for, it might
cause the car to detonate higher in the rev range.

Does anybody have any special insight into the problem?
Looking at the workshop manuals, the earlier 105 cars
maximum advance was supposed to be set at 5100rpm,
compared to 4600rpm for the Alfetta.  Was this because
the earlier cars had more spark advance?  I do know
the later Alfetta's in Australia were detuned a little
to comply with local emissions laws

The car has a bosch mechanical advance distributor in it,
with the points replaced by a Crane XR200 points eliminator
(optical sensor and brain box).  The distributor cap, rotor,
leads, spark plugs and coil are brand new, so I don't think
there is a mechanical problem.  The engine is fresh, with
standard pistons and valves, but has 45mm carbs (too big,
but I'm too lazy to replace them yet, in the hope that I
can make them work better than 40s).

The "kartalamakis" book recommends plumping out the bottom
part of the curve by modifying the distributor with a
VW Golf spring and bending some things that aren't very
clearly explained.  Anybody tried this?

dave.

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