Below should be 2 graphs charting 1k to 6k rpm revs on my carbed 77 308GTB. As you can see the front bank stays at the best AFR of 12.5 in both low & high speed circuit, while the rear bank is as lean as 15 AFR in the low speed circuit & richens up to about 13.5 AFR when on main jets. So what you think could be causing the high AFR on the rear bank? Thanks Bill Image Unavailable, Please Login Image Unavailable, Please Login
I would make sure of the results. Try swapping the leads to the O2 sensors. If you get the same results than try swapping the O2 sensors them selves. If you get the same results check the jets etc in each carb. As a last check could you swap the carb from front to back?
One intake cam could be slightly out of phase compared to the other causing more air to be drawn into the one bank causing the lean condition.
In addition to above, I'd would check to see: 1. Jetting is the same for all 4 carbs (you'd be suprised) 2. No small air leaks at the shaft bearings (common if original never rebuilt) 3. The small filter screens on the carbs are clean 4 Front to rear bank synchronization air flows close; Differences here can cause low rpm mixture differences front to rear
