Husqvarna 531RB Workshop Manual page 50

a) Remove the screws. Disconnect the cables and
remove the top cover.
b) Pull the throttle trigger assembly forward.
Remove the throttle wire.
4. If the product has a thumb throttle handle, do these
steps:
50 - Repair instructions
a) Remove the screw.
b) Pull out the throttle unit.
c) Remove the throttle wire.
935 - 001 -