Ray,
RE: "I did note that the two centrifugal advance mechanism return
springs are
different sizes; I plan to order two "correct" springs."
They are supposed to be different sizes. The smaller spring gives
you
a quick advance just above idle, then the heavier spring provides the bulk
of
the mechanical advance. Look at the end of the heavier spring and you'll
see
that it's "slotted" so that it doesn't start to stretch at all until the
lighter spring has
provided some advance. A graph of advance vs RPM looks very much like two
straight lines joined by a "kink" at a relatively low RPM. The first
segment is
"steeper" than the second.
Having said that, I still think new springs are a good idea. Over
time, the
lighter spring gets stretched out, since it's mostly extended any time the
engine is
above idle. As a result, it starts to provide advance at idle, which it
isn't supposed to
do. You compensate for this by retarding the distributor a bit when you do
a tune-
up, but as a result you decrease the maximum advance available, robbing
your
engine of performance at all RPM. If you can find a shop with an old Sun
dist-
ributor machine, you can check the specs against the bentley manual
numbers.
Good luck,
Tom Marincic
Not a "Spitfire expert" by any means, though I'm (just barely) old
enough
to have driven a brand new one at Alewife Triumph & Volvo in Arlington, MA
in
1980...Thanks, Mom, for coming along and pretending you wanted to buy one!
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