Hi, Bill...
Well, you're using reasonable high-test
unleaded octanes so, so much for this.
As far as the plug heat range goes, go with
Vizard for sure.
My 1098 "CC" ran fine with the NGK "5"' but I think I may have gotten the "5"
heat range from out of an NGK conversion table when I converted over from
Champion "standard tip" N5's (originally factory recommended) to NGK "projected
nose" types. I shoulda read Vizard instead, obviously!! :)
For timing...
my factory manual shows 5 degrees BTDC
for static timing and a dynamic setting of 8 degrees BTDC @ 600rpm, engine
equipped
with the model 25D4 dizzy, ser. #40919.
With the #40919 dizzy,
my book shows 20 degrees of vacuum advance available at the crank between
4-13 in of Hg., which is substantial and
leads me to believe the vacuum advance
on this dizzy is ported to the intake manifold rather than a carb. Is this the
case on your motor, Bill? The foregoing
dynamic timing figure combined with the
following seems to so indicate and if so,
than dynamic timing should be set with
the vacuum advance connected.
My book also shows the centrifugal advance curve of this distributor as well,
vacuum advance DIS-CONNECTED...as follows:
4 degrees @ 1,200 crankshaft rpm
16 " 1,800 " "
28 " 4,400 " "
32 " 5,500 " "
So here's a mechanical curve timing check you can run if you've got a
programmable timing light or know a mech who is suitably
equipped.
And of course, on the mechanical side of
things we have Frank Clarici's post on
"centered" butterflies along with those
idiot spring-loaded butterfly "poppet
valves", if you are unfortunate enough
to have this type of butterfly in your
carbs.
Assuming you have the emission system hoses properly routed and all is well in
this department (?) the only other thing
I can think of would be something mechanical besides what Frank suggested.
Like a shred of a head gasket
squeezed into a combustion chamber or
slight roughness in machining within
or a too "thin" used valve, anyone of which could act as a "hot spot" within a
combustion chamber and cause
"run on" in an otherwise correctly
timed/tuned stock "new" motor running
appropriate octanes.
Cap'n. Bob '60 :{)
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