Your chain will natural stretch. So you will have to adjust motor forward or remove a chain link. If a link is to much go with a half link . Also remove clutch to investigate! Is the clutch or jackshaft making the noise?
Thanks Moto! The chain is rather loose as you say and the bell drum rattles around a lot, not sure if this movement is normal since this is my first experience with 4 stroke engines. I have since isolated the source of the problem to be in the clutch its self. After removing and taking it apart I found lots of grit and some aluminium shavings mixed with grease loose inside the bell drum. After a cleanup and bearing lubrication its operation seems to be back to normal....we shall see.