Ideally it should be run in lightly loaded at full throttle and with the mixture set so it's just barely leaner than the point it switches from 4 stroking to clean 2 stroking (in other words, as rich as it can be but still 2 stroking). An 11x6 prop would be fine for light loading on your 61 and make sure the fuel has some castor in it.

The trick with the mixture is that what the manual says (maybe 1 1/2 turns open) is only a guide. You're far more likely to cause damage running lean than rich so open the needle to maybe 2 1/2 or 3 turns. Then open the throttle (don't hook up the plug just yet) and block the carb with a finger. Turn the prop over about 3 times to draw fuel from the tank and prime the engine. Flick the prop quickly and see if it starts to sound slightly "wet". If it does, then close the throttle until there's maybe a 1/8" gap at the widest point down the barrel and connect the plug.

This next bit you can either do or not, depending how you feel about it. Grasp the prop firmly and turn it moderately quickly over compression and if you feel a bump then it's ready to go (the bump is combustion of some of the mixture inside). Now use the starter and it should fire up quickly. Don't rush, but put the starter safely aside and then open the throttle completely. Chances are it'll be running rich in a 4 stroke so go behind the prop and slowly start winding the needle in until it just makes that clean high pitched 2 stroke sound. That's the setting you need for the running in. If it goes straight into 2 stroking then wind the needle out until you hear the note change to the duller roar of 4 stroking then back in to that 2 stroke. Disconnect the power from the plug and let it run for a minute or so then shut it down to let it cool. It doesn't need to get icy cold, warm is fine.

Restart it (you most likely won't need to prime it this time) at a low throttle and then go immediately back to full throttle. Run out a full tank with these short runs then give a couple of tanks and going a click or two leaner each tank. The thing to avoid is going lean at any time so to make sure you're not getting near the peak setting just give the fuel line a quick pinch and listen for a rev rise. If the revs rise then you're still a little rich which is good. If the revs don't rise then open the needle a bit. Don't listen for a barely noticeable rise, you want a definite rise in revs when you pinch the line.

Now sit back and wait for 129 more different ways to do it