Throttle sticks

I have an older 25hp yamaha tiller motor. When I reach about 50% throttle, it sticks in that position. Advance a little farther and it sticks there, and so on. Very dangerous. Caught me by surprise and almost caused accident. If I quickly open throttle to full, I can force it back to idle. Note, throttle handle works perfectly when engine is not running. Any help greatly appreciated. Thanks
Ferg

[robert graham]

check the throttle friction screw on the tiller handle, check throttle cable, check carb linkage for friction/binding. lubricate all throttle actuating system.

Throttle sticking

Thanks for reply. Have done all except lube. Will try that. As stated all is fine on visual inspection when motor not running. All linkage in excellent condition and operates as it should. Very smooth, no binds anywhere.