The stoichiometric air-fuel ratio (14.7:1) that is the ideal ratio for lowest emissions, but this isn't the best ratio for power. It used to be that 12.5:1 was considered the best power ratio, but with improved combustion chambers and hotter ignition systems, the ideal now is around 12.8:1 to 13.2:1.
I have had Honda XL 650 and KLR 650. Both are larger bore singles than the Duke 390. Neither ran lumpy but then again, neither ran as lean as the KTM 390
alconk don’t worry. You can fix your bike
Whatís a valve train?