MP DISTRIBUTOR TIMING CURVE 340

Moving right along...............

The 340 is on the stand and I was messing around with initial timing. It seems that this engine likes around 25* at idle (advanced timing until the rpm stopped going up, then backed it off a couple of degrees.

I tried manifold vacuum on the VC as @Bewy suggested. It added almost 20 degrees of advance, so I dropped my initial down to 5*. The mechanical is limited to 14* centrifugal for a total of 39* at 3000 RPM (No load).

So if I use the MV, do I set my initial at 5*, then figure out how to let my mechanical advance to add another 29* by 3000 rpm giving me 34* at said rpm while under load.......Then, once I am cruising (light load), the VC adds another 20* for a total of 54 at cruise (actually would be a little less as I will not be cruising at 3000 rpm.)

Am I getting this concept?
Tried manifold vacuum on the valve cover, and added 20 degrees of advance ? Huh ?
Can you explain ? Any pics of the carb hooked up ?