You definitely want to look at your pistons. Depending on state of tune of the motor, you can have staggered jetting (Example: 145 mainjet on rear and 140 on front). An air leak on the left side of the engine could contribute to a lean condition (left bearing crank seal, carb manifold).
_________________
MC28SP, '16 KTM 500EXC, '16 Beta Xtrainer, '07 BMW 1200GS, '96 Ducati 900SS