that username must be the strongest clue
There is this amazing product in Australia that gets tar off paintwork really easily -- and used neat is what the local council uses for removing graffiti from paintwork, bricks and roads.
The manufacturer is Lanotec and the product is called Citra-Force.
It is an industrial strength, water soluble, biodegradable natural citrus cleaner and degreaser.
Start with a well diluted strength and if it needs to be increased just do that . Test an inconspicuous area of paint on your bike first of course.
see
Lanotec | home
It's a specialist product and I had to go to a industrial supplier to get it.