This is usually caused by the clutch slave cylinder. If you remove the slave cylinder from the side of the gearbox (two bolts) and extract the piston from the boot, you will be able to clean and if necessary sand off the nipple which might have formed on the ball of the piston rod. Clean out the dirt and rust in the socket on the end of the clutch fork. Lubricate with some high temp grease (Honda UREA grease) on the ball and socket and re-fit. Ensure the ball sits in the clutch fork socket before replacing the bolts. Replacing the clutch fluid in the system will also improve the clutch pedal feel.