...and I should have added that
tapered roller bearings are much superior to the ball bearings which most manufacturers install at the factory.
There is nothing fundamentally wrong with ball bearings -
when they are new - but their cost and more importantly, their load-bearing capacity is lower than tapered rollers and so they tend to become damaged (brinnelled) fairly rapidly in applications such as motorcycle steering heads. Doing something like a wheelie (not normally a concern with the XS650....
) or hitting a curb will cause an individual ball in the bearing set to "dent" the inner and outer rings (they are actually called "races") and these dents are what cause "notchy" operation - which often results in a wobble.
As noted, the likely best source of replacement bearings is
All Balls Racing - they have bearing kits for just about every bike.
On that issue - everyone should understand that items such as seals, nuts and bolts and bearings - are
standard mechanical components and virtually all OEMs use these standard components. Furthermore, I would say that
none of them (i.e. not Yamaha, Honda, Chevrolet, BMW or Toyota) would ever consider making their own standard mechanical components - so if you can find the correct component sizes and search for that set of sizes - you shall find what you need.
About the only exceptions to these guidelines would be specialized items such as crank bearings, crankshaft seals in 2-strokes - and likely some others that I can't think of right now. However, more traditional applications such as wheel and transmission bearings and seals and steering head bearings are standard mechanical items and they should be widely available.
The beauty of dealing with an outfit such as
All Balls Racing is that they have figured out the correct sizes and load ratings - and packaged the correct components into kits for each bike and the cost is surprisingly low.
Pete