XJ750 Tachometer readings

I have an'83 xj750 seca, that i finally got running again. However while I'm riding the tachometer kind of bounces, but it doesn't match the engine.

For example, I cruise at 80. Sometimes the tach reads around 4500RPM, sometimes it reads 6000rpm, and sometimes it reads almost 9000rpm, but I can't hear any difference in the engine.

So my question is, what is the normal RPM at that speed, and what might cause it to do that? It doesn't seem to do it unless at the higher speed.

 

Check this out:
http://www.xjbikes.com/forums/threads/so-my-tach-died.101660/
Not sure if you have the same tach or not, but your symptoms sound like a good cleaning, thorough inspection and lubrication should smooth things out.

 

I apreciate the reply, but I have an electronic tach

 

Sorry, I'm still learnin' my XJ