I'm trying to figure out what the purpose of vacuum retarded timing
is at idle. The distributor (yes, on my '76 Rabbit, but I think Triumph
Spitfires had this too?) has two vacuum ports: one connected to manifold
vacuum for retard and the other connected to ported vacuum for advance.
Engine timing at idle is about 4 degrees BTDC and swings to ATDC as soon
as you open the throttle.
This is obviously some type of emissions ploy. Perhaps the retarded timing
creates more heat at idle causing more complete combustion? What effect
does this have (if any) on the "smoothness" of idle? I would think
that since the timing is retarded, more fuel/air is required to idle
at the same speed. This implies a lower manifold vacuum which may
adversely effect the carb idle circuit. Or is this all in the noise?
Thanks for listening ... and any feedback that you may have.
Obligatory British car content: I would finished rebuilding the SU
HD8s on the Healey if I could get this sorted out.
--rod.
--
Rod Barman, Dept. of E.E., University of British Columbia
rodb@salmon.ee.ubc.ca
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