The charging system has a tendency to take a dump at the most inopportune time. Insulation on rotor's internal windings breaks down and creates a short. Stators are usually pretty rock solid. Regulator / rectifiers can sometimes go, too. There are some testing procedures using a multimeter in the FSM for each of these components. Rick's Motorsport Electrics sells quality replacements for all of these.
More folks have had issues with the starting system in the last few years, but that's not to say they're all problematic. Age will do anything in. Battery, starter solenoid, and starter can either all be easily replaced or rebuilt as needed. Fresh cables and clean grounds are never bad to look at.
Ignition is relatively rock solid, but as mentioned the ignitors (CDI, TCI, whatever) can fail and simply need to be replaced. Aftermarket options are available. Coils are 3ohm pieces, and aftermarket units are also readily available. I wouldn't consider making some new spark plug wires too.
There is nothing inherently wrong with the cam chain tensioner, but replacements no longer exist. Use what you have while it works.
Carbs are the big thing here. You can get parts just fine, but a lot of folks complain about how hard they are to work on. They're not. Just have patience and use quality parts where needed.
