[alfa] Jon's distributor woes

["Jay Mackro" <jmackro@xxxxxxxxxxxx>]

Jon Pike had asked

>I guess what I'd benifit most from, would be "tightening" the start of
>the curve,  i.e. advancing it such that at idle,
>I could be on the 5deg BTDC mark AND hit the max advance mark when I'm
>at max advance,  rather than be 5-10 deg short like I am now.  I also
>seem to have a lot of "jitter" in my timing mark movements..  don't know
>if this is actual fluttering of the timing advance,  or my old timing
>light stuttering.  Guess it shouldn't jitter no matter what.
>Anyway,  anyone know what would affect the minimum of the curve?

I doubt the jitter is being caused by your old timing light..  There is
probably just one cause for both of your symptoms (jitter in the
timing and failure to advance over a sufficient range between idle
and high rpm).  Could it be that the advance weights are somehow
hanging up and/or flopping around?  Seems I recall Bill Gillham
writing in the Guilia Digest that the older Bosch distributors were
prone to wear on the phenolic plates that the weights rode on,
and this would cause erratic behavior.  My memory is that Jon
has a Marelli distributor, so this may not be the cause, but it might
give an idea for where to start looking.

Does it appear that the weights are all the way "in" at rest? Similarly,
can you see anything that would prevent them from flying all the
way out when spinning quickly?  Are there burrs or wear notches
on the faces of the weight "fingers" that actuate the little rods that
push the shaft and cause the 4-lobed cam to advance?  I guess
substituting another distributor, and seeing how it behaves would
be one way of diagnosing things.

Good luck with it

Jay Mackro
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