tach is fluttering
 

I have 1990 454's with thunderbolt ignition. I put new v.d.o gauges in and one jump's around anything under 2000 r.p.m above it is fine. I switched tach's from port to starboard and get same results with both tachs. does the tach pickup from the coil or the ignition module? Thank's for any imput.

Re: tach is fluttering
 

From the coil ( -) Gray wire.

Re: tach is fluttering
 

I had the same problem with a pair of 525Sc's , I found the rotors were loose on the dist shaft. Merc says to locktite the rotors on. let set for 24 hrs. this fixed mine. good luck.

Re: tach is fluttering
 

I have a single SBC in a Volvo Penta boat and had tach jumpping all around and traced it back to a poor connection. I dunno if it was at the tach, the engine connection or the coil. I cleaned all of them and it fixed it.

Re: tach is fluttering
 

Ditto to what I had.