AFR readings

If your gauge is set up for “straight gas”(14.7:1 stoich), then when it’s reading “13.3:1”, that is basically .905 lambda........ which is 12.75:1 if you’re running E10 gas.

.91 lambda is on the lean end of the normal WOT tuning range for E10.
Try going a little richer and see if it likes it.