Edited on 2013-09-04 9:40:28
Chuck Nissonger has done a fine job for many over the years--but---have you checked the tach generator? That or wiring is the usual issue. As to the generator it has a drive dog that has been known to fail.
Submitted by tvtom@sbcglobal.net on Sun, 09/01/2013 - 23:07
Yes, the internal portion of the tach generator sometime recedes into the housing and the drive dog loses contact with the cam shaft. The output of that generator is AC current so attach an AC meter to the generator terminals while the engine is running..