Okay -- so tuning an engines timing is a function of MANY MANY things and a guy could write a book trying to explain all of that on a forum like this.
Timing is "what the motor wants" ----- and there's MANY things that affect what the motor wants.
Timing is not just @ idle.... it's timing at IDLE and the CURVE and TOTAL timing... and messing with the timing at idle will affect the TOTAL and vice versa....
Gasoline quality and the distributor CURVE and the Tranny/rear gears/tire diameter ALL affect what the motor "wants". Toss in a cam - the cylinder pressures (people call this COMPRESSION RATIO - but that is the WRONG thing to call it) all will affect the timing a motor wants to see.
Having said all of this.... which is why NOBODY can tell you want to set your timing at..... You should look for 10 to 12* at idle... and no more than 36* at 2400 or 2500 rpms with the vacuum line to the vacuum advance disconnected and plugged. Reconnect it when you're done.
Go out for a nice road test -- listen to the motor - for "pinging" under "load" --- so drive it UP a hill and try to lug the motor down. The minute you hear pinging STOP LUGGING IT by selecting a different gear or whatever you have to do. YOU CAN HURT THE MOTOR running with pre-ignition (pinging). Go cruise on the highway -- light throttle pressure - hold steady - try to see if there's any "bucking" or "surging"..... and then just do "seat of the pants" driving if you don't have pinging and you're not surging then just see how it runs and drives.
Remember as your timing is advanced your idle rpms go up - so you'll need to reset that and then check your timing again etc. Also -- as the rpms change - you may need to tweak the idle adjustment screws on the carb.
Best idle adjustment will give you the most rpms and the most VACUUM as read on a gauge... I use a timing light that gives me rpms and I always adjust a carb idle with a vacuum gauge and the timing light (for rpms).
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