I noticed you didn’t use the idle sprockets that came with the East Bay kit but metal pulleys? If they are too heavy they will pull the chain away from being in the plane of the motor sprocket. I used the smaller plastic clothes line pulleys (2.5 inch?).
East Bay shows the white plastic tubes people have used as a chain guide, you’re correct they don’t seem to be mentioned in the instructions.
I searched on “nylon roller” and see someone had a scuffed motor sprocket:
And an example of how someone placed there roller.
