One of the other main features of your air-cooled engine that must be tip-top before a long run....[always carry a spare!!!!]
Personally I prefer to fit a new one before embarking on a long journey as they only cost about 2 or 3 pounds, and its this belt that turns the fan inside your engine to keep it cool! if it dies.. so does your engine! if your battery warning light comes on suddenly while driving along, this is the first thing you should check, DONT drive on if your fan belt is snapped! replace it! but if you've fitted a new one recently check its tension.. press the left hand side of the belt about halfway between the two pulleys with the engine OFF!!! it should push in about 10mm easily, if it goes in more than that, it needs tightening, and if its tighter than that you'll need to free it off as it will knacker your generator/alternator bearings. adjustment is easy......
The back half of the top pulley should have a pair of cut-outs in it, you need to stop the top pulley from turning by putting a flat screwdriver, or a small flat chisel into one of these slots between it and the generator. once it stops turning you can then undo the nut in the centre of the top pulley.
Remove the washer under the nut and keep any shims that you find underneath that to one side. the two halves of the pulley should then separate, and you can replace the belt if necessary. if your belt was too tight, you will need to put some of the shims you found under your washer between the two halves of the pulley to increase the gap between the two halves, if it was too loose, take some of the shims out from between the pulleys!... simple really!
Once your happy you can remove the screwdriver/chisel from the back of the pulley and reassemble the pulley.[don't forget to put those spare shims back under the washer!!] then tighten the nut with your spanner/socket allowing the pulley to turn as you do this [this stops the belt getting caught up] once it is nearly tight, check the flex of the belt is OK [this is trial and error, you may have to repeat if you get the tension wrong].... and put the chisel back behind the pulley for the final tightening... bingo! one sorted v-belt! grab another beer!! RTTS is looming!!