[embee]

Second the "Sid Squid adjustment" advice.

Also check that it's not overfilled with oil. Check it when the engine is hot, stop the engine and wait a couple of minutes, hold bike upright and check the window. Mid way between max-min is ideal.

The oil type can have an effect too.

Check the worm drive at the bottom end of the cable is in good condition too. Very simple to check, you can do it before adjusting the mechanism according to the Squid. Loosen the cable right off, undo the 2 bolts holding the worm drive in place, take it off and unwind the housing from the lever part. It should be well greased and all the balls should be present. If it's rusty/worn, then replace.