To throw in another 2p (2d in the hardware world?), run-on is also a
problem with early cars. My experience has been that if the carbs
are tuned well (mixture, synch'd), run-on is pretty usual at idle
speeds above 1000 rpm. As later engine specs called for higher idle
revs for lower idle emissions with smooth idle, the anti-run-on valve
was added. Opening/blipping the throttle on shutoff performs some of
the function (sometimes) of the valve--upsetting the mixture enough
to stop Diesel combustion. I try to keep idle speed up as close to
1000 rpm as I can without run-on so the generator light doesn't burn
too brightly at stop signs, on a rainy night, with all the electric
gizmos (technical term) running...
Chris Attias
'64 MGB
'84 Alfa Romeo GTV-6
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