Hmm they changed the gear shape in what about 76? tranny has to be changed as a set can't recall the reason offhand. Not to dis your efforts but really I don't have any "out of the ordinary" issues shifting, finding neutral on any of my XS650s.
Yep, spline change in '77, polished shaft outers instead of shaft inners. Less binding friction for the sliders thataway.
Your input is actually significant, so no "dis" inferred. It's helpful, more of a confirmation of my suspicions. Numerous subtle/secret tranny changes up to '77.
Pretty much all multi plate wet clutch setups to this day will drag the pack at a stop. A quick slight release of the clutch lever, pull back in and tap the foot lever for neutral, done. That "tap" the lever may often be missed No matter how finessed, a steady press won't work as well rather a light tap up of the boot gets the lever to move that "just right" amount that stops in the neutral notch.
That's right, some degree of drag, even on the Honda clutches. But, their shifter mechanisms were more tolerant of that drag.
Kawasaki uses a neutral finder that blocks second gear when the bike is at 0 MPH so a solid stab up still stops at neutral. I like heel shifters, not least because I can tap down to find neutral. My BMW K bike with a single plate dry clutch had a very easy to find neutral even after 130K miles
There's an idea. If I had enuff room between the 2nd wheel and case, I could codger up a type of 'blocker' that would engage a finger on the shiftdrum, kinda like a sear block.
Summarizing my thoughts. The XS650 engine came from an advanced design (for its time in the '50s) Hosk. The Yamaha engineers inherited this new-to-them 4-stroke, and had to make it work.
The intro model had tranny features that were a bit unusual, compared to others, like Honda. And, these features went thru multiple changes up to 1977.
A few tranny/shifter/clutch unique items and changes that I can think of:
Intro 70 - Roller pins for shiftforks, not alongside the guidebar, narrow shiftfork guideholes, oiling holes in the guidebar, combo clutch frictions (plastic core and aluminum core).
1971- Separator o-rings added to clutch
1972- Deeper 1st gear (which would increase drag loading on 1st dogs), solid shiftdrum revised to multipart shiftdrum with bearing behind starwheel, which would reduce shiftdrum drag from stopper, neutral detent, and shifter claw.
1974- Clutch changed to 7-plate frictions, all aluminum core, separator o-rings dropped.
1976- Last year of the roller pins in the shiftforks.
1977- Spline changes, polished outer versus polished inner.
The tranny gears up to 1977 had anywhere from zero, to one, to two indicator notches. Some of those gears went thru as many as 5 revisions. Unknown stuff there. Trying to derive undercutting info from XSJohn's (rip) posts, I get the impression that undercutting of 1st and 2nd may have been discontinued on the later trannys, and that would reduce fork loading at gear disengagement.
Last rambling, from what I saw of the customer base back then, the abusive, go-fast, missed-shift crowd would've moved over to the next 'hot' bikes after the mid-70s, leaving the XS650 to the more mature, sedate, metro-riders. Which means fewer complaints and warranty work, stabilizing the model's tranny config.
All the above stuff leads me to think that Yamaha was doing a lot of behind-the-scenes tranny/shifter fixes on the early models to solve the shifting and well-known 'neutral finding' issues, as noted in some of the period publications. What I recall of the neutral-finding issues on this forum seem to be mostly on the pre-77 models.
My world here is strictly 256, the '71 XS1B. What I'm suspecting here is a trans/shifter mechanism that's barely tolerant of the shifting loads caused by clutch drag, and enters into 'bind' mode quickly. That shift disengagement measurement test I mentioned earlier would be a way to find the 'knee' in the curve, the transition from sliding parts to binding.
This 'binding' is the same principle used the sliding jaws on pipe clamps.
Sorry for being so terse, avoiding writing another book...
