Join Date: Mar 2001
Location: Tucson, AZ, USA
Yea.... I would agree with the other guy who posted...JohnZ has good advice...
This problem is pertubative...meaning that it chases it's tail and gets worse..
The lower you put the base timing...the idle lowers and gets rougher...now you crank up the idle screw to try to bring up the idle and then you start getting into the primary circuit, thus leaving the curb-idle circuit useless...this makes the butterfly open further which in turns can make for a engine run-on after the ignition is shut-off....
Try doing the opposite.... Bring the timing up in the 10 to 12 range, then turn the idle screw down to bring it to normal idle...now you might see the idle getting rough or wanting to cough and spit and stall..this may be that you now need to properly adjust the idle-mixture screws to maximize the rpm and vacuum ....
As for detonation while you are driving...that is not a function of your base timing...you need to adjust the tab in the distributor so it does not advance as much mechanically....also proper spring selection.
Are you running vacuum advance????
If so...make sure to disconnect it and plug it when doing the timing..
If your not running vacuum advance a normal set-up for your 327 engine and timming would be 18 to 20 degrees of base timing at 800 RPM idle with a mechanical advance kicking in about 1000 to 1200 RPM and ending with about 12 degress advance fully in by about 3200 RPM...
This would be a total advance of about 32 degrees....adjust the total advance stop-tab to stay just below the detonation point..
Generally a cooler plug, a richer jet, and a lower thermostat all help in keeping that detonation point from creaping down a degree or two...this all depends on your situation.