ORIGINAL: Moms Mistake

Generally speaking, close the main needle and open it 2, or 2 and a half turns. Be careful when closing the main needle as closing it too hard can damage internal parts and you'll have real problems, you may have to buy a new main needle if it gets damaged. Start the engine and keep a close eye on the temperature. I usually keep the temp around 190 and 210 degrees. Buy a temp gun, It'll be worth every penny. The temp should never read 250, 230 at the most if you want the engine to last.

Run several tanks through the engine while keeping an eye on the temp. The quicker the throttle response, the more it's being broke-in, or running-in as some call it. As you notice the engine being broke-in, give the engine full throttle and turn the main needle clock-wise until the highest rpm is reached and immediately turn the main needle counter-clockwise until you hear a decrease in rpm, that tells you it has the right air/ fuel mixture.

Next, give the engine full throttle and point the aircraft upward and downward 30 degrees and listen for increases, or decrease in rpm. Slight decreases, or increases is ok, if the engine stops running, the low speed set screw on the carberator needs to be adjusted richer, or leaner, thats all....

Keep in mind, engines run richer on a stand still, or on the ground, because of prop pressure and run leaner in the air, . Stay on the rich side until you gain experience.