How do I make it...smoooooooth???

------------------
91RS, 305, 5-speed, black with pearl white racing stripes. Not that it matters, but K&N airfilter and flowmaster exhaust

 

you can start by calling it a tachometer, then go check all of the connections under the hood.
Its the green wire usually on the HEI.
My friend had a similar problem on his IROC and after his tune up the motor ran smoother and the tach operated like it was supposed to

------------------
91 RS W/carbed 350, Vortec heads, performer rpm, Comp cams Xtreme energy 280 grind. BFG Drag radials. 3.42 posi,Corvette servoed 700r4, ****ty stock converter
13.24@104

 

Moving to the "Electronics Forum". You may have better luck getting your answer there.