I run my sport gassers where they just barely transition...Anything leaner and the engine dies when the throttle is opened..If that's "very lean" so be it..[8D]
The high is set just at peak rpm and then backed off very slightly, not 4 stroking...
The racer 289 is set for 850 degrees F on the exhaust temp when wide open in the straightaway, low speed is not an issue..As long as it keeps running after a heat race anything goes, it's way rich on purpose to cool it off... Works for us.....