You'll prolly get lots-o-replies on this one.
One way, without a timing light, that I've used--but not on a motobrick, yet--is what I call, "road timing". Fill the tank with whatever gas you want to run. Set your timing where you think is best. Take it out on the road, stick it in something like third or fourth gear @ ~2500 rpm and roll it on hard. If it pings, you'll need to retard the timing a bit from there. If it doesn't ping, you can advance the timing a bit from there. I usually continue in this fashion until I have it where it does not ping but if advanced any more it will. If you're uncomfortable with that setting, you can always retard it a smidge from there for insurance.
A timing light is great but this method of timing gets you where you can have the highest advance, w/o pinging for the octane of gas you want to run. For a touring bike, I prefer regular as it is cheaper and some places you may end up, will have two pumps, one labeled, "Diesel" and the other labeled, "Gas". I can assure you, the one labeled "Gas" does not dispense "Super".
Just one way to get there,
Tom