The last couple of Months there has been a Tsunami of owners trying to adjust 'Idle TIming' and fiddling with the sync between spark and throttle in an Attempt to set the Idle speed. And it gets a little tiring/frustrating
Most 3rd Party Service Manuals are not even good reading material for the Outhouse, and the paper is too slippery to use as Wipes.
Since there are often changes from year to year on engines, a model specific service manual is really the only way to go as it will explain what every adjust screw/threaded rod is for.
If the carbs are the same size(venturi bore, as well as throttle bore, it doesn't mean the fuel flow calibration will be correct before or after a Jet swap. If the carbs came from a 50 HP or a 60 Hp, the calibration may have been different because of differences in Exhaust Tuning(again, what applies to 2 stroke engines is different than to car/truck engines), Off Idle fuel delivery could be different, etc etc etc.
It was mentioned above about a Displacement change, that happened in 76 when the 41 cubic in. 50 hp became a 44 cubis in. 55 hp. In 1980 the 55 hp was upgraded to 60 hp, same displacement(internal changes though)
Factory manual has been ordered from eBay. The block has a plug with 55el77d on it so definitely a 1977 block. 2 strokes are a new thing to me other than repairs on small single cylinder weedwackers, leaf blowers, etc.