Translations:KAVAN AP06A - Instruction Manual/81/en

3) With the engine running at full power, carefully lift the nose of the airplane about 45° into the air. The mixture should not become too lean, but you may hear a slight increase in R.P.M. This is good. If the engine sags, or loses R.P.M. when you hold the nose up, the mixture is too lean and should be set slightly richer. The engine should always exhibit a noticeable smoke trail from the exhaust.

Note: R.P.M. will increase about 10% - 30% in the air. This is due to the forward motion of the aircraft as it is flying. Because of this forward motion, more air is entering the carburettor, at a higher force, and causes the mixture to lean out. Additionally, as the fuel level in the fuel tank goes down, fuel draw becomes more difficult for the engine, especially during aerobatics, also causing the mixture to go lean. It is imperative that you set the mixture rich while on the ground to compensate for the leaning tendencies that will happen in the air. Always watch the exhaust during your flight. The engine should leave a noticeable white smoke trail at all times. It there is no smoke trail, the engine is running too lean. You should land immediately and reset the mixture.