I WAS READING MY OWNERS MANUAL YESTERDAY AND I NOTICED THAT THE BORE & STROKE WERE IDENTICAL FOR THE 90,115 AND THE 140. SO WHATS THE DIFFERENCE?IVE HEARD STORIES ABOUT HEADS CARBORATION AND EXHAUST. IM LOOKING FOR THE EXACT DIFFERANCE ON THIS MODEL. IF IT IS SOMETHING THAT I DEEM DOABLE ID MAKE HER A 140.