Hi folks.  Well, I wired in my new-to-me stator & coil assembly today (see my other post about all the lights not working, which I seem to have diagnosed & repaired) so now I'm ready to set the timing and point gap.  I bought a dial gauge and have no problem finding top dead center.  The thing is, I'm at a complete loss as to what I'm looking for on the gauge (image attached) as to where 3.2mm BTDC is.  I've read the service manual and watched a few videos, but I just don't know what the markings on this gauge refer to and how many revolutions and/or hash marks on the dial I need to find this elusive 3.2mm BTDC.  The small needle on the gauge does nothing more than go from "0" to "1", so I don't know if that is normal or not.  I have my little "tester" bulb all connected and the bulb does in fact go dim (and ultimately out) when the points open, but I just need help as to what I'm looking for and what the numbers mean on the gauge.  Sorry if I sound like a complete idiot, but to be honest....my '75 Hodaka Road Toad was much easier to time, as it has a hash mark on the flywheel and engine case and all I had to do was break out the ol' timing light...LOL.   Thank you very much for any help you can offer.

Umm, i'm thinking & thinking. Hope others can sort it, but i 'think' it's a really coarse scale with 10mm travel--i think--so 3.2mm is two marks past the number 3. says 0-10mm on one side of the bit by the needle center, but then says 0.01mm "zero point oh one"on other side opposite & that is very small like 4 tenths of a thou. My heads spinning lol. I'd be tempted to measure say 3mm on a long nail down the plug hole & mark the flywheel to the case. Then insert dial gauge, find tdc the go down to your mark & see how the dial gauge reads. Then you'll understand the scale. HELP someone.

That gauge has a range of 1 to 10 mm .
Find top dead centre . the small hand needs to be reading about 6 , so adjust the height of the gauge thus .
Then zero the large hand by turning the outer .
Turn the magneto rotor clockwise 3.2 complete large hand sweeps , and that gives you 3.2mm BTDC .
At this point the small hand will be at 2.8 .
In short the big hand counts a mm per rotation sweep .

Thanks guys.  One mm per full rotation of the large needle then.  I'll give that a try.  One other thing that is confusing me is how you actually do the "adjusting" of the timing.  I have a few mechanic friends who are telling me that I'll need to rotate the entire stator plate via the 3 screws in their oval holes.  The Yamaha service manual though only mentions loosening the one screw that holds the contact breaker (points) assembly and moving it slightly one way or the other, and makes no mention whatsoever about moving the entire stator plate.  I'm wondering which method is correct?  I have the 3 stator plate screws dead center in their oval holes now.  Are those holes oval shaped to adjust the timing, or just to allow for adjustment due to wear over time...or something else?

The timing is done with point gap adjustment . At least on the older enduros .
The older ones didn't have an adjustment on the stator plate .
Once timing is set , you then check max point gap is within spec .
If my advice isn't relevant with your model , someone more familiar with later 250's
will correct me .

Like I've said, center the slots pretty much.  You might be able to see marks where the factory screws were tightened.

Then adjust the points to get timing right.  Pretend the slots don't exist! 

This is important for a good spark.  The coils and magnet relationship when the points open needs to be correct for max voltage and spark.  This happens on your bike for the stock timing specs when the slots are near centered.  If you start rotating the plate from where Yamaha had it, you start getting a weaker spark. 

I think the 250B has a slotted plate. Pity you can't get at the screws without pulling the flywheel so i wouldn't tighten it fully until ya sure & hopefully won't alter with final tightening. I'd just set it 'or leave it' where its been for 50 years & you will see the screw marks possibly near the center. Then i'd loosen the points just enough to tweak then in the screwdriver slot of the points & get them "just breaking' at your 3.2btdc. Then check the open gap & in theory they should be near 12-15thou. If the gap is to wide or too close then you need to decide which way to move the plate then try again by setting them to break at 3.2.

Sorry Mark, didn't mean to jump in. Yours wasn't there when i started typing haha.

Thanks for all the great information guys.  I do believe I 'get it" now, and will be setting the timing in the morning.  Hopefully it will be easy to find that sweet spot and the bike will once again run as it should!

Well...I got the timing set and the bike runs great!  Thank you all for your help.  I was actually unable to use the dial indicator that I just bought because one of its rods was too short and one was too long...so I just marked TDC and 3.2mm BTDC on a small skinny screwdriver and used it as my "measuring device."  Apparently I must have been either spot on or close enough because as I said, the bike runs great.  Sadly, as has been the case with this bike since I got it 2 weeks ago, as soon as I fix one issue, another one pops up.  As I returned from the test ride today after setting the timing, my buddy noticed that my tail light would "flash" along with the turn signal when I would activate either the left or right turn signal switch.  I honestly thought I had all the wiring sorted out, as this never occurred when I tested the turn signals with the bike not running.  Then, after I turned the bike off and tried the signals again (just running them from the battery), all lights were dead and I saw that I had blown the main fuse off the battery.  The wiring from the rear turn signals and to the tail/brake light is all going to be redone tomorrow and I'll look for good clean grounds on all of it.  Also, I just replaced the flasher relay with the one sold on eBay by "pobit", as it was supposed to be much better than the OEM relay.  Anyone here have experience with the relays he sells?  I'm hoping to sort out this issue tomorrow so I can move on to the next issue....the non-functioning tachometer!