I bought an electronic tachometer (ametek dixson 700 series)off of ebay. I thought I had connected it correctly to the harness under the dash. I set the tach for 100 hz from the Sender (2 notches in the dampener x 3000 RPM top speed / 60 sec). The tach only reads about 450 RPM at idle. What could cause this inaccurate reading?

 

What's it read foot on the floor in neutral? These things will idle at 450 RPM, but you can't see out the mirrors.

 

That's another thing... Foot to the floor takes the needle back to zero. I stop when the needle goes 360 degrees because I do not want to ruin the guage. There is no smoke at idle, either.

 

I'd try some other settings.

 

THey all make the reading too high or low...None are just right. Settings that seem acceptable lose accuracy when you watch it while you are driving