any advice on removing the rear wheel bearings on my DT1B?  Manual shows to use a special Yamaha tool.  I'm thinking of making one from an old Philips screwdriver if I can figure out the size of the hole in the bearing spacer, or open to other ideas.Thanks

I think DEET makes that tool.

There should be posts on here from others that have made something as well.

I don't ever recall using one but looks a good idea. But if the picture is true to how it 'is' [& only has one supporting ring] you could easily force [might be loose but shouldn't be] it over on the unsupported end then come in from the other end & tap the bearing out because you'll then have enough of the bearing exposed to drive out.--if that makes sense when you un-jumble it lol.

I've replaced tons of wheel bearings on the old enduros from 68 to 78 and no need to use a special tool. Just a regular tapered punch. The spacer inside has a girdle in the middle allowing the spacer to teeter a bit. Just teeter it down a bit on one end and then the punch has a place to land on the bearing. Never knew there was a special tool because never needed one. Never damaged a hub or bearing.

Thanks! I’ll give that a try next week when I get my new bearings. 

Ideally, the centering ring on the spacer should not be centered side to side on the spacer... it's easier to "teeter" it if it's not... and because it's not centered, try from one side and then the other if you can't move the spacer enough to get a bite on the edge of the bearing... once bearing moves a little, it gets easier.

Tips... 

Barring any manufacturer instructions to the contrary, axles should always be installed from right to left with nut on the left side of bike (nut on left side when sitting on seat facing forward.)

As I said, the centering sleeve, washer, whatever you want to call it, is offset to one side of the spacer.  I always put the spacer in with that washer closer to the right side of the hub.  This does two things.  First, since the axle enters from the right side of the hub, centering washer towards that side makes it easier to get axle in if spacer moved a bit while axle is out.   Second, I always know that inserting the punch from the right side of the hub first will be the easiest side to get the spacer to tip a little so I can get the punch to catch the edge of the left bearing...  also remember not to tap in one place...  move the punch around and try to keep the bearing square to the hub as you tap it out. 

While bearings are usually easy to tap out...  you need a long, fairly skinny punch.  A skinny brass punch will usually bend. 

I bought a tool kit to replace my bearings on my CT1C rear wheel. The large tube was not quite wide enough diameter-wise to push against the wheel. I ended up using a fork seal driver tool to get it to work.
Those things are really in there so take your time and make sure you are not damaging your hub while pulling them. There are some YouTube videos on how to do this. Good luck! 
Got my kit on eBay for $30.00. Kinda cheap but did the job.
 

Another tip:

Use HEAT.

A handheld propane torch played around the bearing area for a few minutes will allow the metal to expand just a bit. That will substantially help bearing removal and replacement. Don't be afraid to get it pretty hot, you cannot get that hub hot enough to actually warp it. Use a long tapered punch like Mark says, get the bearing area good and warm, and you will surprise yourself with how easy the bearing comes out.

Installation is the same, only better. Freeze the bearings first. In fact, before you remove the old ones, put the new ones in the freezer (overnight is even better). Heat the hub up and using the axle to guide the bearing it will usually almost drop in. Let it cool down (allows the hub to contract around the new bearing) and do the other side. I have used this method for years. What I like is that I am not stressing the new bearings much if at all installing them like this.