Return ATU (advancer) to correct range

[5twins]

As far as I know, yes, they're all the same. In my mind, one of the issues with this set-up is the sharp corner on the slot that pushes the weight tab back to the retarded position. Over time this sharp corner starts cutting into the side of the tab .....

Although I haven't tried it, I've often thought maybe rounding that sharp corner off a little might reduce the wear on the tab, or at least slow it down. But it would probably increase the amount of advance too so you couldn't take much off, just "break" that sharp corner, round it off just a little bit.

 

[grizld1]

Expanding the bob weight tips isn't the only way to skin this cat, maybe not even the best way. gggGary suggested attaching shims to the limiting tabs; I like that approach a lot. I corrected one advance governor back in the late 90's by having a thin layer of braze applied to the tops of the weights where they contact the tabs, then filed off the excess to get a 25* curve. BTW you don't have to get all AR about an exact 25* curve. Most of us find that these motors run more happily with full advance anywhere from 36* to 38* BTDC, and if the spark at full retard hits at 17* instead of 15* it will still be in the "F" range. Reducing the range slightly won't hurt a thing.

 

[TX650A Van Islander]

Thank you for the input. This, as with all of this bike rebuild, has been an interesting learning curve. Attached is a photo, not that great, of the flattened tab, prior to the peening. I just secured a "new" pair, from a local guy, so will go from there.

 

[gggGary]

I'm not aware that they ever changed.
Yamaha 256-81653-10-00 GOVERNOR ASSEMBLY carries an "early" part number and is listed for all years that used points.
https://www.partzilla.com/catalog/yamaha/motorcycle/1970/xs1/cam-shaft-chain-tensioner

 

[TX650A Van Islander]

Update on this project: I shimmed out the limiting tabs with tape until the engine didn't run past the full advance. I measured that thickness of the tape, and built up the weights with JB Weld to the same thickness. It is now almost getting to full advance, but not beyond, as before. It seems to be running well. I am planning on monitoring this with my timing light going forward to ensure that the JB Weld isn't wearing down. It does seem quite hard.
I threw in another photo of my two air-cooled 650s looking fine. So different and yet so similar.