If you follow the gear cables
to where it changed the gears on the engine
(gear box, near shaft) it will be connected to a lever. If you disconnect the clip holding the cable to the lever you can move it back and forth with your hand. Generally up is neutral and then forward and backwards. Alternatively just watch the lever while someone else moves the gear back and forth from the throttle/gear lever on deck
. If you can move it into neutral by hand, with the cable disconnected, then it is likely your cable which tend to stretch or get damaged by resting on something hot on the engine
. If it's the cable this is cheap
and easy to fix. You just have to make sure the length is the same, or at least close to the cable you've removed. Undoing the cables
is easy and you shouldn't have any trouble.
Let us know the results