The bike would not always downshift reliably. About 70% of the time pressing down on the shifter did nothing and a second try would usually get it to shift. The lever always returned to it's centered position but there was no resistance that lets you know something inside the tranny is moving. It could happen in any gear and was most disconcerting when braking/ cornering /downshifting.
After searching and reading, I concluded I needed to pull the oil pan and see what was going on. Wrong. At least on this model pulling the pan only lets you see the shift drum and gives access to the neutral detent.
Here's a photo of the shifting mechanism that lies mostly behind the clutch basket.
The shift shaft was not returning to a full centered position which wasn't allowing the downshift pawl to engage the next notch in the shift drum. There was a few mm of play where the two fingers of the return spring straddle the stud.
This is a pic of the shift shaft removed and looking at the backside where the return spring mounts. The left finger of the spring pushes the shifter to center after upshifts, while the right one returns it after downshifts. I bent the right finger very slightly to the left in this picture. Maybe 1 mm. Just enough so when it was installed there was no play between these fingers and the stud they ride against.
That's it. Simple, huh? However you do need to remove the entire clutch basket and foot shift lever to get access to this spring. And it is a tough little bugger. I had to clamp the spring itself in the bench vise and use vise grips to get that tiny bend. But she downshifts every time now.
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