Engine running lean on one side.

[COPPERN]

The plugs are reading very lean, sensors and leads were swapped side to side and changed to verify the were working properly and fuel pressure was at 7.5 pounds using 2 differernt gauges. I will look for a possible vacuum leaks next. Thank you to everyone who replied .

[Adger Smith]

If this is a new combination w/new or un used carb you may have Hi speed A/B's that are too big. Check all sizes of the A/B's (Hi & low) before going any further, just to be sure. They may have done an unintentional swap when doing assy of the carb. I lost the main bearings of a nice 565 on the dyno because it was very lean in the middle (17-1 AF) of the pull. It took 2 1/2 pulls to detonate enough to hurt the bearings. It ran through the lean area and was 13. 2 A/F up high. It was because the carb builder left the A/B's for the intermediate circuit out of the carb. We thought the new carb was OK and didn't even look at it when installing it on the Dyno. I now check everything on the carb before starting with a new unknown/tested combo.