Motorcycle Repair: 1987 1100 sportster, piston rings, valve guides

Question
When I start my bike everything runs fine. When I have driven a mile or two I stop and white smoke appears out of the back cylinder exhaust. I have completely rebuilt my super E S&S carb. I also remove the spark plug of that cylinder and it burns clean. any suggestions.

Answer
Your probably starting to burn some oil, but not enough to show on the plugs. Your oil would either be coming from the valve guides or the piston rings. Start with a compression test. Your two cylinders should be within 10% of each other. If not then you need to do a top end job.
Good luck and happy riding
Mike