What sort of restoration are you talking about ? What are the the problems you have noticed ? Is it burning lots of oil ? Rebuilding the four cylinder engine is quite a challenge because of the number of parts you have to find first. The engine has to be taken out to be refurbished, so take this opportunity to get your starter and alternator refurbished too: they are easy to access with the engine out.

This is a great bike, I loved it, but I could not afford to spend over 2000 on the engine alone.