Good Initial Timing and Too much Total Timing Problem. Seeking guidance to minimize total timing. 1969 Swinger 340 4 Gear

Cubzy said

Shouldn’t initial timing(12 in my case)plus mechanical timing(haven’t tested this yet)=all in timing(57 in my case) 12+mechanical timing=57deg. Therefore my mechanical timing is 45deg which would be the mechanical timing. This sounds like way to much? What am I missing?

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What you are missing is that you are including the vacuum advance! Your total timing is your initial plus the mechanical advance in the distributor. Let's just say 20 degree. So 20 plus your 12 initial is 32. Now you have the vacuum advance adding even more. So 32 plus 25 in the vacuum equals 57. You have two timing advance situations going on. The vacuum advance works off you ported vacuum so under load the vacuum dropps and your timing will go back to your total without the can. That's why you have to check timing with and without the vacuum can hooked up. Hope that helps