I have been working on an xl125s ('80 I think, possibly '81) and it was nearing completion and my dad found an xl185 '79 engine for sale. It seems like a no brainer upgrade but does anyone know if it is a simple straight swap out? Does anything need changing? Also, what should the engine cost? The guy is selling it for just shy of what I paid for the bike, so either I got a deal or 185 engines are rare?