"No, you should warm it up at
"No, you should warm it up at idle and then do your adjusting, slowly, allowing it time (15-20 seconds) to adjust to the change you made and then leave it alone.
If it stumbles after it's set that could indicate some crud in the carb or a bad gasket etc which usually requires pulling the carb, cleaning it out and throwing in some new gaskets.
But it could be an old spark plug as well, so change unless new.
The "tilt pin" or "thrust pin" (you can choose your term) can be set to trim the motor properly for the boat you have it on.
It's usually a case of playing around a bit - set it, see how it works, move it up or down one pin spot, try again - to see if one spot works a little better at getting the boat up on plane etc - but with a small horse motor it normally doesn't make a whole lot of difference..."