if your issue is the belt, it is a little bit more than just looking at it.
you can measure the width of the belt at the top (widest part of the belt) and tell us how wide it is.
then there is the rollers in the front pully.
In the pully there is about 8 rollers that are nylon covered steal rollers, they each sit in a grove and it is their job to change the bikes gearing go higher as you go faster!
You have to take off the front pully and make shore that the grove where the rollers "roll" from slow speed to high speed is clean and dirt free.
Also you will notice that the rolers are (used to be) white, and the outer edge will be dirty and brown/gray. this is impregnated dirt stuck on the rollers. give the rollers a good clean up with a kitchen scourour in the kitchen sink (note, do not let the wife see you do this!)
when the rollers get very dirty they get too grippy and have trouble moving in the pully against the retaining plate.
the symptons of this is a bike that will feel like it is "stuck in 3rd gear" when taking off (ie sluggish) and somtimes they can be stuck in "4th gear" when they should be in "6th"
if you know what I mean with the gearing, because the bike has a million gears being belt driven auto!
a normal LTA700 or 750 can take off and do a very nice wheel stand at every take off.
But as the rollers get dirty it can get to the point where a LTA700 just cant do a wheel stand any more!
if this happens not to be your problem, do for the snorkle restricting the air in to the airbox.
other wise, because the bike it a 700 and maybe has a few Miles on it by now, you could have a clogged fuel filter in your fuel pump.
I am not saying this because I sell them at my website! I am saying it because the LTA range of bikes have a good pump, and a good fuel filter, but it is a very small fuel filter and is very prone to clogging with what every people put in to the tanks!
Normaly people find that a bike with a clogged fuel filter is hard starting and a flat spot above idle, then some top end power loss.
maybe you should do a fuel pump flow measurment to see how much is flowing.
just ask if you need help to do that (or consault your workshop book)