I installed a Demon Cycles tach 2 summers ago with the suggested single fire adaptor made w/ Radio shack parts. Has worked great up until a couple of weeks ago. I notices that when I first started the engine, the needle would bounce from 0 to pinned a few times before settling into the correct RPM. Now it has started doing it and won't stop. Has anyone else had this problem. Could it be that a resistor failed , a loose wire, or is the tach shot?