Is this a simple fix?

 

your speedo cable.

 

I thought it would be a sensor or something. hard to fix?

 

Have you been working under the hood near the transmission? Maybe even have had the speedo cable disconnected for any reason?
Or have you been working on the dash and have had the cluster out?

Usually the jumpy speedo is from a cable that's not connected properly.
Most commonly it's somebody that had been working on the transmission, disconnected the cable, and then lost the clip shown in this image when reconnecting
http://i294.photobucket.com/albums/m...Face/crx/4.jpg
That's an easy fix.

If not, then you can try shooting some lithium grease into the cable, but I would just replace it.
Not super hard, but if you aren't comfortable removing the cluster then it's probably something you shouldn't do.

Here's a walk though on a CRX.
Same thing with Civic
http://crxcommunity.com/viewtopic.php?t=43624

 

I believe it got stolen into before. the center console is diffrent. under dash fuse cover is gone. and i noticed he changed out the ignition coil when i changed the dizzy cap. So yea its possible he couldve done that