Definition of self-control: the stepped headers / section 1 showed up on Saturday and this is what I’ve been working on:
My wife’s ‘76 CB400F, almost ready to ride again.
Although I did take some time to tune the idle and tip-in on the Zed. I realized after some frustratingly weird results that the car was idling perfectly at 900RPM when warm because the guy who was working on it didn’t understand how the IAC’s PWM table works*, and had tuned the 0 throttle section (and I’m guessing, unfortunately, the rest) of the VE table around the IAC being permanently at around 65% open. Now the idle hunts and bounces around a bit but it will actually do it when cold and the engine doesn’t hang lean coming off the throttle due to unmetered idle airflow. VE tuning is a bit weird - feels like changes have the opposite effect to what I’d expected - but I think I’ve got the hang of it now. Higher VE == expectation that cylinders contain higher % of their volume at a given RPM / throttle position == more fuel metered by the ECU. So it’s just like tuning a fuel table, when for some reason I had it mapped exactly backwards in my mind. Hooray for WBO2 sensors / gauges!
* for anybody doing this later: the idle subsystem uses a “guess->measure difference->weight inputs->guess again” loop for setting the idle valve position (0-100%). If using a stepper-based IAC, there is no magic except telling it how many steps == 1% in the setup wizard. When using solenoid-based systems, you need to set up the appropriate output tables for PWM frequency vs. idle position and PWM duty cycle (i.e. percent of time solenoid gets power) vs. idle position. Then you need to set the idle base position table, which is vs. idle position as well - in my case, this is 0 across the board so the IAC is closed unless the idle circuit sees RPM falling when it believes the car should be idling. Then it’s just tuning the idle position PWM duty cycle table and the feedback loop’s calculation weights to get it to idle smoothly, whereupon you can set the target idle vs. coolant temp table to get a nice high idle when cold that settles to a nice low idle when warm. Ta dah