Base timing at operating temp, at set idle speed ( so your carb has to be set for mixture and idle speed first), with the vac advance disconnected should be 12deg BTDC...with about 34 degs all in ( still no vac advance hooked up) around the 2500 rpm range. An advance timing light is required obviously, and your starting points maybe out to lunch, your distributor might not go all in until 2600 rpm, but that will get adjusted later. some engines will like a bit more...some will like a little less. A keen ear is needed to determine the max amount with out detonation. I prefer to set all in timing, and as long as the base timing falls somewhere around the 12 deg mark ( lets say 8-14) then good as long as it starts well.base timing is used only during starting, and from the factory mechanical and vac advance where preset in the distributor for best emissions and fuel economy...so setting base brought the other numbers to facorty specs IF the distributor is up to snuff...springs get weak with age, weights bind up, and vac cans leak over time.like most things there is room for improvement and better performance through fine tuning.if you set total and the base comes in at 18-20..you need to carefully lengthen the fly weight slots in the distributor, as you arent getting enough mechanical advance. if you set your all in and the base comes in below the 8-10 mark. you need to shorten the fly weight slots ( mig them up a bit). Once you have max timing set and the base falls in line, then you can play with the springs to set up when and how fast the timing comes in...usually for the street two step in is optimal ( one light spring and one heavier...this will let one fly weight move out first and advance the timing some, then as rpm builds, the second weight will start moving out starting the second advance step and the combination of the 2 springs should have all the advance in somewhere around 2400 rpm mark..again all engines a little different). With out a distributor machine, this is all trial and error and can take a bit of time for someone not proficient at it. Once you have that all dialed in, THEN you can hook up the vac advance and you can start to get your cruising, light load timing dialed in. Different vac canisters have numbers stamped on the side..that is the amount of vac advance it will provide. some cans also have a little allen head screw in the vac nipple, they have an adjustable range. basically you want as much vac advance as the engine will take under light load with out detonation ( highway driving, light accel with out down shifting and not letting the engine drop below 5 or so hg...no vac and the can isnt working)
