Timing added by Vacuum advance with the initial set at 9°BTDC.
View attachment 1715651716
Timing added by vacuum with the initial set at 18°BTDC.
View attachment 1715651722
Compare the timing at 1500, 2000 and 2500 rpm with moderate to light loads.
Big difference?
Can they both be providing the most efficiency and power for the load and fuel mixture?
Could one of them be advanced so much that it causes pinging in that rpm range?