Had ignition trouble in an embarassing place? Does your ignition still have any point to it? (sorry) Here's a quick rundown on how to check it out:
This can work for either twin or single cylinder motorcycles, the main difference being that the twin has two of everything, the single only one. Extrapolate!
First, make sure the points are clean by pulling a strip of clean business card or match folder through them when closed. Check to see if it gets oily, keep doing it till it doesn't. Then test the circuits as follows:
Advanced or retarded timing shouldn't make any difference to whether or not it sparks. Get one cylinder sparking at a time. One of your point sets is closed (the one you just cleaned.) Put a clean piece of match folder between them, and then "jump" the other one with a screwdriver. When you open the circuit by removing the screwdriver the appropriate plug (out of the head and connected to the coil) should spark. If it does, you know your ignition circuit, coil, HT lead, plug, and probably condenser are OK on that side. Repeat for the other side by moving kicker until these point close and the others open.
If there was no spark, check to make sure that there is a primary spark when you pull out the screwdriver. If not, pull the + (point) wire off the coil and then use a test light to see that you have juice to the - (hot) side of the coil, and then check the empty + terminal for light - coil continuity. Ignition switch on for these two, of course. Then ground the + terminal with a jumper wire, you should get a primary spark here when you unground, and the plug should spark at the same time. This tests the ignition circuit, the coil primary, the HT wire, and the coil itself.
If you're OK so far, now check to make sure the points themselves are breaking the circuit like they're spozed to. Do this by reconnecting the - wire (point side) and pulling the closed point open, looking for a spark. If you don't get one, the wire is broken (unlikely) or the points have been put in with an insulating washer in the wrong place (real likely) In very odd cases, the a clean set of points may become nonconducting. I've only seen this once in my whole life. If so, you'll get sparks by jumping open points with a screwdriver, but not when you pull closes ones open with ignition on. Do them both, if they work, then you know the points are conducting and making sparks.
If you can't get a consistent spark with both plugs in this fashion, it's time to check the points for pitting, dirtiness, etc.
Those round cans you asked about are condensers. They are connected in parallel with the points on each side, and in rare cases can be shorted. Disconnecting them while doing the above tests will rule out this possibility; if reconnecting them kills the sparks on one side, then you know that condenser's shorted. Their purpose is to mellow out the make-and-break of the points, cutting down on the spark arcing and making the points last longer. Excessive burning of the points one one or the other side indicates the condenser's bagged. On cars, the normal thing was to replace the condenser with every point replacement, but bike condensers cost more, so I don't.
So, tht's about all there is to care and feeding of your ignition points. If this is too formidable for you, you may elect to spring for a transistor box to replace them with a different setup - a "reluctor" and a magnet where the points used to be, which "fire" a box full of transistors and other solid-state esoterica. The only problem with these is that they're impossible to fix on the road, so to be safe you should carry a spare. For that kind of money, you can afford to take taxis, so just leave the bike at home. Suit yourself, but have fun, whichever way you do it