Neil,
I've pretty much eliminated the ignition as a factor in the wierd
Colortune readings. I have a Pertronix electronic ignition replacing
the points--dwell set by the electronics in the Hall-effect switch.
Both vacuum and centrifugal advances are working. Putting the
timing gun on it, the timing looks dead even--no jumping around.
Valves set to stock .015 intake and exhaust cold. I have been using
standard SU dashpot oil--Penrite, and did the test with a fully warm
engine at 68 degrees F. air temp.
The two unknowns so far are the cam pattern/condition and the
California Reformulated Gasoline. The cam thing is only a theory at
this point--that greater valve overlap changing the nature of the
proper mixture enough to change what you see through a Colortune. I
would think the problem on my car would be with cam pattern rather
than wear, as the same condition is observed in all cylinders. Has
anyone with a hot street cam or race cam set their carbs with a
Colortune?
Last and best thought I've seen came from Bob Howard--that California
gasoline, formulated with MTBE and other oxygenates, alters what you
see at the correct mixture point. Evidently this has been a point of
discussion with serveral people. Maybe I should import some 49-state
gas and try this one out!!
Chris Attias
'64 MGB
'84 Alfa Romeo GTV-6
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