My bike jerks at 30 mph, which I believe is a result of running too lean. It has been worse since the most recent tune-up. I suspect the tune up was geared to max power rather than drivability. I could just take it back to the mechanic but there are some practicality issues with that. (Its 3 hours travel.) So the question (hoping not to sound really dumb): can the low-speed mixture be adjusted with some adjustment screw or is it all done digitally?