Thanks Mattax, that was interesting information. If I am understanding it correctly, the motor liked 18Initial/36 degrees the best and dropping to 17/35 not only hurt power, but narrowed (and lowered) the torque curve. I did notice that advance timing (36 or 37) didn't seem as different at upper RPMs, and that 37 was maybe even better. Judging from what I am seeing, It looks like it liked 18 degrees at initial and liked a little extra total advance at the upper RPM ranges. I see what you are saying about the A/F changing with changes in timing. What I found interesting was that as timing was reduced, the A/F appeared to get leaner. Not what I expected for some reason. I guess I always expected more advance to show up leaner, not more rich So am I reading the last graph correctly that 4000 RPM (WOT start) is designated by the vertical line going up just to the right of "11.5" on the bottom access? I'm guessing that from the way the A/F changed and low vacuum leveled out. So tell me this,... Am I correct in assuming the reason the A/F went rich at that vertical line is because the secondaries kicked in? I am assuming that because of how the A/F stayed more stable running primaries only. You mentioned above that mixture should go leaner as throttle is opened, up to 70-90% throttle, then go richer. Can you explain why that is? I would expect just the opposite, or is it because opening the throttle opens the butterflies and lets more air flow through the carb?