There was some problem with the tach that caused a lot of needle-bouncing thus making it kind of annoying and non-useful. It had something to do with some characteristic of the Suzuki bikes that the tach's weren't accommodating.
If you connect it to the correct wire, it should be smooth all through the band. I'm saying this cause when I was at the Dyno, he tried connecting to the plug wire, and it behaved as you described. It would be smooth until about 3rd, then go hay-wire.
He connected to the primary coil wire under the seat on my bike, and it was smooth all the way through about 8000 rpms.