I know someone had this problem before but I can't find a fix in the archives. I have a 1986 that I bought used, it hadn't been running for over a year. I've finally got it running, new maintenance free battery does wonders for hard to start bikes. Now my tach jumps all over the place. At idle it seems to be reading about right but when you open the throttle it actually goes to zero and then bounces all over the place. The bike doesn't feel like it's misfiring on either cylinder and the throttle response is good.