Mine just started acting odd like this today. I had the same problem about 2 months ago. After a couple times stuttering and even stalling, I couldn't get bike to turn over. I assumed battery, when I went to remove it, I bent the negative cable at the attachment point, and got power. Seems to have been a not so good connection at the battery. If your mechanic unhooked the battery, he may have fixed it by accident?
Good luck
jeff
