I believe I'll have to call BS on this one.
>Yes, emissions, but also a smoother running car at idle for the mass
>(American) market. An engine running with a lot of advance at idle is
>difficult to adjust for a smooth even idle. In Europe, drivers are
>typically more enlightened about sporty cars.
Based on your response, I'd have to agree.
>then expected them to be as smooth and trouble free as their Detroit
>grocery getter.
As I recall, all the American Iron from the 60's, Mustangs, Chevelles
have the timing set to 8 to 12 BTDC. The centrifical advance brings this
up to 25 to 30 BTDC at 3,000 RPM. The vacuum advance adds some more
advance for cruising, falling off as soon as you hit the gas.
I don't recall ANY American Iron using a vacuum retard during the 60's?
>Vacuum retard pulls off some of the advance at idle only.
And between each gear change, any time you release the trottle and create
a high vacuum, I'd call this built in hesitation at best.
What I've seen has nothing to do with this design, its the wear in the
mechanical pieces causing the retard thing to torque the plate, changing
timing and dwell in the process. With this mess, there is NO way to
tune the car. The right, original answer is a new distributor. One
alternative is disconnecting the retard and changing to EI. I like
this one as it eliminates the "symptoms" and eliminates the timing flopping
around needlessly. Given everything else is "normal", this works well.
I'll let some of the physics types explain to you why the best performance,
smoothest running, and best gas mileage is produced by firing the plug
PRIOR to the point of maximum compression. Something to do with the
propagation delay of an exploding gas.
Roger
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