Rich Idle AFR reading

stumblinhorse said

Thanks for really helping out. The curves and instructions are located here:
https://static.summitracing.com/global/images/instructions/sum-851003.pdf
Quoting:
The factory installed medium blue springs in this distributor, generate a performance ignition advance curve that typically begins at 1200 RPM and generates 22-24° crankshaft advance; that is fully in by 3200-3300 RPM. This mechanical advance curve will work in most street performance engines.

Click to expand...

With 12* set at idle of 750 rpm, it will still be 12* at 650 or 700 rpm. That is good. Unfortunately you may also find it is still at 12* all the way up to 1200 rpm. However, that description doesn't match what you found, which was it hit 34* by 2500 rpm. If the advance did what is in the instructions, it would be:
12* at 750 rpm,
12* at 1200 rpm
34* at 3200 rpm (12* + 22* )

There's not quite enough info in the instructions for me to be sure of what's inside. The advance degrees adjustment is similar to a Mallory YH mechanism. However the springs offered are similar to a Delco mechanism. With a YH mechanism, changing the the slot length (degrees of advance) changes the initial spring loads. The little graphs don't help because 3 of them use a different amount of advance than the others. I prefer not to guess, or go on and on about different types of advance mechanisms, the limitations and how each of them may be adjusted.