Yes do check the stud. Some are press fit, others threaded. I suggest adjusting them all when the engine is at idle. But first, use this to get you in the ball park:
To adjust the valves, it is vitally important that the cam lobe for the valve you are adjusting is on it's base circle... the round part of the egg shaped cam lobe, not the pointy end.
INTAKE VALVE ADJUSTMENT: Rotate the engine by hand until the exhaust valve rocker begins to push the spring down on the cylinder your are adjusting. That puts the intake valve cam lobe on it's base circle. Adjust the nut while trying to move the pushrod up and down or twisting it. As soon as you feel a slight drag, and I mean SLIGHT, tighten the intake 1/4-1/2 turn more.
EXHAUST VALVE ADJUSTMENT: Rotate the engine again by hand until the intake valve compresses fully and moves 1/2 way to 2/3 of the way back up. This puts the exhaust valve on it's base circle. Adjust the nut while trying to move the pushrod up and down or twisting it. As soon as you feel a slight drag, and I mean SLIGHT, tighten the intake 1/4-1/2 turn more.
Only do this for the cylinders that are having problems.
Then, start the engine. Loosen the adjusting nut on the valve you want to adjust slowly until you hear it make a TAP TAP TAP noise. Then slowly tighten the nut until the tap sound stops. Now add 1/4 turn tighter. You may notice that it takes a moment for the engine to stabilize when you add 1/4 turn. This is normal. Move to the next valve and repeat until they are all adjusted. Button up the VCs and go boating.