A lot of what you're asking depends on the current condition of your bikes.
First off, what tires have you got on now? How many miles on the bikes?
How many miles on the chain and sprockets? How old is the battery?
Patrick's Holy Grail of Survival
Three things that you must have right:
2. Chain & Sprockets
If you leave with worn chain and sprockets (and it sounds like you may not
know a worn chain from an Empanada
) or a weak battery then THESE things will cause you problems down the road. Deal with them NOW.
If the chain is even looking slightly knackered, change it now while you have access to parts..... and BE SURE to fit new sprockets as well. Don't cheap out on this, please. Get the best chain you can find/afford and only STEEL sprockets. I prefer DID X ring chains. (VM if possible) Yamaha stock sprockets are fine.
If there is any doubt about the current battery.....then
I would go with a NEW Yuasa battery, hopefully a sealed, MF, glass matt style
battery. Cheap insurance. Get the best you can afford.
Tires: The Other bugaboo.... Hopefully your tires are fresh? If you're running knobbies then your tires will wear fairly quickly on pavement. Tire pressures
(depending on WHAT tires you've got) should be adjusted for either dirt
or pavement riding. So this means you need to carry a bicycle pump. Check your tire pressures EVERY MORNING, right after you clean and check the chain. EVERY DAY!
Some rough psi guidelines for that bike with your load:
Dual Sport tires
Pavement: F 27 R 32
Dirt: F 20 R 26
Pavement: F 30 R 34
Dirt: F 22 R 26
Be sure to carry plenty of spare tubes and good patch kits and irons.
Flats will be one of your most challenging delays. Have you practised
changing tires? You know how to do this I hope?
Chain: I hate chain lube. I only use it in rain. Otherwise 90 wt. gear oil (available everywhere) will do. Keeping a CLEAN chain is the key to long life.
Never run any sort of lube when riding off road. If fact, stop and wipe down
all oil off your chain before you enter dirt. Run you chain dry in dirt, it will last
longer. A Daily wipe down with only light oiling on the street is the way to go. DO NOT over oil, its just not needed. In heavy rain, you will need to oil every 100 miles or get a Scott Oiler or use chain lube. Keep it adjusted too. Get help
with this, its critical and must be set to be correct when the bike is fully loaded with you ON IT.
Maybe someone else can detail chain adjustment?
Keep an eye on it. If your bikes' have been modified there is a chance the airboxes may be "opened up". Look to see if this is the case. If the air boxes
are open then in dusty conditions your air filter will get dirty much more quickly. An air filter can get dirty is a short time in very heavy dust. Wash out
with Diesel (wear rubber gloves), wring carefully, oil lightly, re-install. Your filter (if oiled properly) can stand quite a bit of dirt. You can wait till its pretty much covered in dirt before cleaning, but not too much.
If you can, make sure the fork oil is fresh and correct level in the forks.
Check rear sag with all your gear on the bike. Let the bike stand loaded.
Measure from center of rear axle, straight up to frame or seat. Note this #.
Now SIT on the bike with feet on pegs. Full weight on the bike. Have your buddy measure same distance. If its more than about 3 inches difference between two figures, then you need to crank in more preload or get another spring (unlikely). So crank up the threaded collar on the rear shock until you've got about 2.5 inches of sag if possible.
Get to know and love your carburator. Get down there and just stare at it.
Learn it. Find the litte screw at the bottom of the float bowl. This will allow
you to drain the float bowl if you get water or crap in the fuel, which will end up in the carb. Install an inline filter. (Auto type is fine)
Learn where the idle control is. Learn how the throttle cables route and how
they hook onto the carb. Keep area clean.
Look at the color of your brake fluid. Is it dark? If so, change it out. Buy a
NEW, sealed can of brake fluid with the correct Dot rating (DOT lll or DOT lV
Pump all the old fluid out as you add new fluid. Never let fluid resevoir get more than half way down. Use bleed bolt on brake caliper. Do NOT crank down
too hard on this bolt. Open and close bleed bolt to pump out old fluid. Do front and rear systems.
Coolant? I thought XT600's were air cooled? 660's water cooled.
Look for bodged or mickey moused wires or connectors. Make sure everything
works. Carry spare fuses. If you are running heated gear make sure you don't kill your battery. Don't leave key on with headlight burning when you stop.
Its culumative. Turn off ignition...always. (man, so many guys screw this up!)
I would start pulling off the headlight fairing and getting familiar with whats
behind it. Take your time. Learn it. In the pitch dark, on Ruta 40 with a
50 knot cross wind and rain is not the time to learn your wiring layout.
Que le via bien,