Optimize the spark curve for a SlantSix.
The above graph shows the acceptable advance based on the specs in the FSM.
1 bbl carb was all that was offered that year. A carb with more capacity should allow the engine denser air at mid to high rpm with the throttles fully or nearly fully open. This combination should burn faster and therefore need a little less timing under those conditions.
This is why rpm is so important.
You can make small adjustments to the spring tension by turning the spring perches. The perches are mounted as eccentrics. More tension on the primary spring will delay the advance so it starts at a higher rpm. Earlier tension on the secondary spring slows the advance sooner.
Two other quirks that may be cause pinging.
What is the status of the EGR system?
The EGR valve should be closed when the air temps are cool, and when the throttle is nearly wide open, and IIRC at idle.
The slant six did not use ported vacuum for determining the throttle at idle or near wide open.
Instead it used venturi vacuum. Doubt your new carb has a way to connect to that.
Finally, what is the status of the CTO? That's the coolant temperature switch which was in some (all?) OSAC setups. If the coolant was getting over 225*F, it switched the vacuum advance signal from ported to manifold vacuum. If coolant temps are staying reasonable I wouldn't worry about it, but is another little gimick that was needed with the retard timing for the early emissions systems.
That shows in the shop manual as the original distributor for a 225 with automatic that year.
The above graph shows the acceptable advance based on the specs in the FSM.
1 bbl carb was all that was offered that year. A carb with more capacity should allow the engine denser air at mid to high rpm with the throttles fully or nearly fully open. This combination should burn faster and therefore need a little less timing under those conditions.
As you can see from the graph, the advance is very quick above 750 or 800 rpm.
This is why rpm is so important.
You can make small adjustments to the spring tension by turning the spring perches. The perches are mounted as eccentrics. More tension on the primary spring will delay the advance so it starts at a higher rpm. Earlier tension on the secondary spring slows the advance sooner.
Two other quirks that may be cause pinging.
What is the status of the EGR system?
The EGR valve should be closed when the air temps are cool, and when the throttle is nearly wide open, and IIRC at idle.
The slant six did not use ported vacuum for determining the throttle at idle or near wide open.
Instead it used venturi vacuum. Doubt your new carb has a way to connect to that.
Finally, what is the status of the CTO? That's the coolant temperature switch which was in some (all?) OSAC setups. If the coolant was getting over 225*F, it switched the vacuum advance signal from ported to manifold vacuum. If coolant temps are staying reasonable I wouldn't worry about it, but is another little gimick that was needed with the retard timing for the early emissions systems.