[TomO]

could just be the O2, but also the intake ports for the Z1 are really small and the Z1 intake manifold is the best to use with it in order to keep the airspeed velocity up. This promotes good swirl in the combustion chamber which also allows good burning of the lean mixture. the injectors worry me a bit as well since the Z1 uses 190cc injectors stock...you may be squirting too much fuel in the chambers.