Well there are not that many possibilities to consider. 1 an loose or broken cable is the most likely problem. look to see first if the outer sheath is connected at both ends. if not bingo, you found it but, if still attached you need to loosen it from both ends to check the actual flexible drive cable is not broken. I know, 80 some hours seems to be unlikely that it would break but I had one recently with about an hour on in break so it can happen. the ends are unique to one another, at least most models are, a tab on one end and a square shaped end on the other. Its never a bad idea to service it while your working on it.
Its just like do a mechanical speedo on a car or truck. Slide it out, add a coating of a good grease. White lith is a great choice here. slide it back in, then... make sure the end of the drive cable is seated ***all*** the way into the tach drive on the engine. it could fool ya! then seat the cable into the tach head (meter/indicator). Tighten the outer sheath firmly as they could become loose. carefully tighten if you decide to use tools other than your hands! the outer sheath ends are aluminum and kinda soft. So be careful not the deform them.
Give it a try, fixed it ok. If not, most likely the tach head.
good luck,
kytim
