Makes sense, in that I'd suspect that whomever is in charge of the calibration for those carbs probably isn't told the intended application is 500 cubes making 600++ HP. Yeah, the bigger engine would create more signal than the carb was originally tuned for, whereas a too-big carb would need to be richer to crutch the lack of signal. [/quote]

Spot on Brad , the too rich I encountered with the Modman and 440ci . Seen it a few times on the dyno , raw fuel/black smoke but AFR showing lean .

Tex[/quote]


Probably because it was misfiring. If it missed or half fired, all the oxygen that should have been used up during combustion but didn't goes roaring out the exhaust and right by the O2 sensor which has no choice but to do its job.

Kevin