Just changed mine last night on a 618, don`t know if the 718 is the same set up. This how I changed mine.
1st, unhook the positive cable from the battery.
Remove the 2 shaft covers/guards.
Remove drive shaft/ 4 bolts/nuts.
Remove fan from the right hydro. ( standing at rear wheel looking towards hydro`s.
Removed the idler pulley from the right side. 1 bolt/nut, make sure that you don`t loose any spacers that might be behind the pulley.
I used a pry bar to hold the left idler pulley up, but you could take the spring off.
Remove old belt.
Here comes the hard part! You will think that you have the wrong belt, I think that every time I change it out.
Put the belt on the left hydro pulley, under the left idler, over the center pulley, and then comes that really hard part!
Place the belt in the top of the right hydro pulley, hold it down in the pulley while you turn the pulley clockwise with your other hand until it pops on.
It will be really hard to turn the pulley, but don`t give up ! took me 4 tries to get it on last night. But now my hydro`s are working great.
Good luck, Tommy