Tachometer problem

I need some wisdom. My tachometer works fine to about 6K, then the needle just kinda bounces back and forth. Sometimes it will bounce and then go up to where I'm at( say 9K) but not often. Whats the problem and can I fix it? or do I need to replace parts/whole thing??

I would try lubing the tach cable. The inner cable can be pulled out of the sheath, cleaned, and lubed with a coat of motor oil. That may help. Ed