There is also a useful technique with a tach that a newbie can use to learn what rich and lean and too lean sound like.

Crank the engine and open the throttle.
Open the needle valve until the engine starts to run obviously rich. There will be lots of exhaust and it might even have raw fuel in it. The engine will have obviously slowed down as you get it into "obvious" rich. It may even sound like a 4cycle engine. Tach the sucker.

Now, start to slowly lean it out.
Watch your tach readings as you lean it out.
The rpm will increase as you continue to lean it out.
The engine will continue to turn better and better rpm.
Turn the needle in slowly. Don't hurry.
At some point, as you continue to lean the needle out, the rpm will begin to fall off.
You've just discovered the max rpm of that engine and the too-lean needle setting.

The max rpm needle setting was your too-lean needle setting.
Somewhere richer on the needle is your optimum setting.
Back the needle out a few clicks and note the tach reading. Now, with that setting, hold the airplane with the nose pointed up. If the engine sags after 10-20 seconds, click the needle out a couple more clicks. If you can't get the needle rich enough that the engine will hold it's rpm with the nose up, you've got a tank problem that you need to solve. If you can, you're good to go.