Your starter for 10:
I have a clamshell with a late 80s / early 90s set of decals on the lid.
Having dismantled a sizeable chunk of it, what I find hints that it's an early 80s "650" machine, and based on a few trawls round Ishop's microfiches, (They are American, so may not match what we were buying in Europe back then) I reckon the engine could fall into one of three serial number ranges (the original ID has long gone).
4382057 THRU 4571651
7073473 THRU 7087822
9112989 THRU 9135824
Having compared a good chunk of the powerhead & major components of the leg & gearbox, I cannot find any differences in part numbers for the major components.
So, the question - are these three series of numbers all for the same engine, but with different decals? or were there more subtle changes that triggered the number series change? - or was it just a different Model year?
If there were subtle changes, what were they - I'd like to make sure this rebuild has all the changes Merc made for maximum reliability!