Need Opinions. Have nothing to compare to.
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.
Yes. That is how I interpreted it. To know the curve better, I'd have to go back to see which distributor was on the engine during those runs, and whether I checked the full curve later that week. Since I was paying for time, I did the minimum to have reference points.
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
I'm not well enough steeped in the combustion or the sensor operations to explain it myself! I remember reading debates and discussions about how oxygen sensors work and if CO effects them directly. Certainly when some of combustion results in a different proportion of CO to O2 than is normal, the O2 sensor alone will not know that. The post by Shrinker (earlier link) was after those discussions and much more investigation. (Me, I just watched from the sidelines). Another anamoly (sp?) in the chemical balance that widebands can't know is from a misfire. I think they (WBO2) are great tools, but I thought it worth showing some situations where they should not be believed.
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.
Yes. Mostly from the vacuum going to near zero. With only two barrels open, it then when up slowly with the higher rpms.
(Sorry about not identifying the bottom axis as time in seconds. 11.5 seconds from beginning of the logging session)
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.
No. It went rich because the power valve opened when manifold vacuum dropped below 8.5 Hg.
These particular runs were with a '750 cfm' vacuum secondary carb with plain spring IIRC. So based on some other runs, I'd say the secondaries were not fully open at 4000 rpm. With mechanical secondaries of course they will be fully open when the primaries are fully open. The purpose of the secondaries is less restriction at high rpm. As long as fuel distribution isn't hurt, this is more efficient.
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?
Probably better, I'll requote from Racingfuelsystems and other forums. I would have just posted the link, but Tapatalk took over the hosting and screwed up all the preexisting images and attachments. :( It makes it hard to hard read.:mad: