Re: schwin spedo
Is that the $10 one from wal-mart? It works fine on my bike. The only problem I had was that it would reset itself everytime I started the motor during the colder months. In the summer there are no problems. I would try rerouting the wires away from the coil, and mounting the speedo as far away as possible from the engine. You are getting electrical interference.
If all else fails, get an EMP blocker from Radio Shack.