Not sure quite what setup you're running, but if it's like mine with a spider and a chainring bolted to it, then would moving the ring to the other side of the spider help with chain alignment? Also, curiously enough I found that putting the ring on back to front made some improvement.
The other thing I did was to have the bike upside down, and slowly rotated the pedals backward to see how each tooth on the ring took up the chain. I did find a couple that it wasn't smooth to the point of lifting the chain off the ring, and attended to these teeth with a file (gently) to ease the transition. The reason for running the chain backward was that, like yours, it would more often than not come off when back-pedaling.
Oh, yes and the spider I bought to go with the chainring was a 'cheap as chips' ebay job, that I discovered had one arm out of line, and so was causing the ring to deviate slightly, now replaced for a better one.
I hope some of this helps.
The other thing I did was to have the bike upside down, and slowly rotated the pedals backward to see how each tooth on the ring took up the chain. I did find a couple that it wasn't smooth to the point of lifting the chain off the ring, and attended to these teeth with a file (gently) to ease the transition. The reason for running the chain backward was that, like yours, it would more often than not come off when back-pedaling.
Oh, yes and the spider I bought to go with the chainring was a 'cheap as chips' ebay job, that I discovered had one arm out of line, and so was causing the ring to deviate slightly, now replaced for a better one.
I hope some of this helps.
)
