rpm drops

[xt performer]

Hi again mates:

I was riding my xt and i saw the rpm in the dashboard like i always do,and i realized that the RPM engine in the dashboard were a little bit low in the dashboard,something like 150 rpm more or less,and i could feel the ENGINE was a little bit higher about rpm judging it with my hearing and the velocimeter.

What can be wrong with that?

I saw the tachometer cable that goes to the engine and i know this acts mechanically,for counting the rpms.

Is there some maintenance to this cable like lubing?

if so, because of lack of lubing, could this affect the rpms?

thanks,any help would be welcome