@spychic any NEW tire is going to be 'heavier' than an old worn slick tire....plz keep that in consideration...it's the 'flywheel effect'..,increased by tread material.. also, the starter button control over time oxidizes, and gets 'dirty' like the Nintendo NES cartridges used to do...i know a few riders(not just NX'ers) that have similar issues..and by repeated squeezing and holding while depressing the button, and moving your thumb all around will re-polish the contacts inside the switch control... (or take it apart and use some emery paper) I'm not saying that IS your problem, just that you might be over-thinking it<, due to the perception of the heavier rear tire, deflection, and the flywheel effect... I don't think a bad CDI caused any delays in engagement of the starter, only a non-start when the engine turns over.. The 'increased vibration' could be from the new tires diameter lifting the rear axle, and putting more weight on the forks, increasing whatever vibes by subtle changes in geometry... I would check fork fluid condition and levels, check fork tube in the clamps, etc.. if it's suddenly become excessive? The good news, the more you ride, the more wear, the lighter the rear tire ! And the Duro median is not just bigger, it's a HEAVY tire for it's size...heavier than other models of the same 'size'.... sorry for any confusing brevity, i broke two cars last week, and i'm hardly making complete sentences after failing to fix one. .