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My 1978 tach sits on the needle until I get up over I would guess about 3500 rpms then it runs up to redline and drifts back down. Any ideas what is going on there?
First thing to do is eliminate the tach filter. Remove both ends and put the tach connection into the distributor. No need for any interference. If still the same then need to look into the tach circuit board. Lots of links in the above post.
The tach filter does not give interference to the tach dial but rather prevents interference from HEI ignition (spikes)
And it protects the tach's sensitive circuit board from damage.
If someone does not need the filter for some reason, good for you, lucky.
But to the rest of us, do you want to take a chance the absence of the filter will not fry a circuit?
