that and make sure you have at least 35psi of fuel pressure. but when i had my z i had to clean the connectors every 6 months due to corrosion.
then i got smart and used dielectric grease AKA (spark plug grease). no problems after that.
ya time for a new tach. before you do if you have a friend with a cheap tach hook the signal wire up to it and see if it does the same thing. if so you have other issues.