Acetone works pretty good on spray paint. Just wipe it on and wipe it off after a few minutes. It takes a while but you might be able to keep the clear coat.

If it were me I would disassemble the entire bike and remove the paint with some heavy duty airplane stripper. This would also remove the clear coat (which is probably pretty scratched up anyway) but then you could polish it and put some wax on it to really make it shine.